fix: sweep legacy /userguide /cite /icon-info /linking-to-us URLs; fix __ heading pattern; .md fallback in content service (closes #82 #76)

Two long-tail CMS rendering problems addressed together.

#82 -- landing-page modules and legacy URLs:

  Rewrites legacy URL prefixes in MDX content to match the migrated
  /documentation/* tree (same sweep style as #88 did for /dev/*):

    /userguide      -> /documentation/userguide
    /dev            -> /documentation/dev
    /cite           -> /documentation/cite
    /icon-info      -> /documentation/icon-info
    /linking-to-us  -> /documentation/linking-to-us

  Catches relative, paren-wrapped, angle-bracket-wrapped, and absolute
  (https://reactome.org/X) variants. Touches 46 .mdx files.

  Three landing pages had a `####  __[ Label ](URL)` heading pattern
  that rendered as literal `__` text because the underscores sat
  outside the link, so addJumpCards.ts couldn't pick them up. Flips
  them to `#### [__Label](URL)` so the underscore-prefix-inside-link
  pattern (the same one graph-database etc. already use) triggers
  the link-icon transform. Affects:

    content/documentation/index.mdx          (3 modules)
    content/community/index.mdx              (3 modules)
    content/documentation/userguide.mdx      (3 training links)

  Verified with chromium --headless --dump-dom: /documentation now
  renders 3 .link-icon instances on the page where there were 0.

#76 -- accept .md as well as .mdx:

  content.service.ts now tries .mdx first, then falls back to .md.
  Single-line additive change with rxjs catchError. So the CMS
  pipeline accepts either file extension without forcing renames.

npm run check:nav-options stays green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: adamjohnwright

projects/website-angular/content/about/news/109-new-advanced-search-available-in-our-pathway-browser.mdx

@@ -21,4 +21,4 @@ The new search features:
   4. Filtering results by one or more entity types (i.e. Proteins, Chemical compounds, Reactions, etc.)
   5. Flagging a given entity to persist its highligthing.
 
-To learn more, please check the [Searching Reactome](</userguide/searching>) section in our [User Guide](</userguide>).
+To learn more, please check the [Searching Reactome](</documentation/userguide/searching>) section in our [User Guide](</documentation/userguide>).

projects/website-angular/content/about/news/125-version-68-of-reactome-is-now-online.mdx

@@ -19,7 +19,7 @@ tags: ["about", "news", "125-version-68-of-reactome-is-now-online"]
 
 **Tools and Data.** Our services and software tools are designed for biologists, bioinformaticians, and software developers. Pathway data is available to view in our [Pathway Browser](</PathwayBrowser/>), to [analyze](</PathwayBrowser/#/TOOL=AT>) your own dataset, to [download](</download-data>), and to access programmatically through our [Content](</ContentService/>) and [Analysis](</AnalysisService/>) Services. The [ReactomeFIViz app](</tools/reactome-fiviz>) for Cytoscape provides tools to find pathways and network patterns related to cancer and other types of diseases.
 
-**Documentation and Training**. Visit our online [User Guide](</userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
+**Documentation and Training**. Visit our online [User Guide](</documentation/userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</documentation/dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
 
 **About the Reactome Project**. Reactome is a collaboration between groups at the Ontario Institute for Cancer Research, Oregon Health and Science University, New York University Langone Medical Center, and The European Bioinformatics Institute. Reactome annotation files and interaction data derived from Reactome are distributed under a Creative Commons Public Domain (CC0 1.0 Universal) Licence. A Creative Commons Attribution 4.0 International (CC BY 4.0) Licence will apply to all software and code, database data dumps, and Pathway Illustrations (Enhanced High-Level Diagrams), Icon Library, Art and Branding Materials. A full description of the new and updated content is available on the Reactome [website](</>).
 

projects/website-angular/content/about/news/137-version-69-released.mdx

@@ -20,7 +20,7 @@ tags: ["about", "news", "137-version-69-released"]
 
 **Tools and Data.** Our services and software tools are designed for biologists, bioinformaticians, and software developers. Pathway data is available to view in our [Pathway Browser](</PathwayBrowser/>), to [analyze](</PathwayBrowser/#TOOL=AT>) your own dataset, to [download](</download-data>), and to access programmatically through our [Content](</ContentService/>) and [Analysis](</AnalysisService/>) Services. The [ReactomeFIViz app](</tools/reactome-fiviz>) for Cytoscape provides tools to find pathways and network patterns related to cancer and other types of diseases.
 
-**Documentation and Training**. Visit our online [User Guide](</userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
+**Documentation and Training**. Visit our online [User Guide](</documentation/userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</documentation/dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
 
 **About the Reactome Project**. Reactome is a collaboration between groups at the Ontario Institute for Cancer Research, Oregon Health and Science University, New York University Langone Medical Center, and The European Bioinformatics Institute. Reactome annotation files and interaction data derived from Reactome are distributed under a Creative Commons Public Domain (CC0 1.0 Universal) Licence. A Creative Commons Attribution 4.0 International (CC BY 4.0) Licence will apply to all software and code, database data dumps, and Pathway Illustrations (Enhanced High-Level Diagrams), Icon Library, Art and Branding Materials. A full description of the new and updated content is available on the Reactome [website](<https://reactome.org>).
 

projects/website-angular/content/about/news/138-orcid-claim-your-works.mdx

@@ -13,4 +13,4 @@ Reactome is a curated database, it critically depends on the expertise of curato
 
 Because we appreciate your work contribution either authoring or reviewing a pathway or reaction, we have now made it easy to claim your contribution in ORCID. Using this new feature that has been integrated into our website, contributors who have provided their ORCID ID can, by simply clicking a button, reference their work in their profile.
 
-Follow this [link](</userguide/claim-your-work> "Click for instructions on how to claim your work") to learn more about how you can claim your work.
+Follow this [link](</documentation/userguide/claim-your-work> "Click for instructions on how to claim your work") to learn more about how you can claim your work.

projects/website-angular/content/about/news/142-version-70-released.mdx

@@ -19,7 +19,7 @@ tags: ["about", "news", "142-version-70-released"]
 
 **Tools and Data.** Our services and software tools are designed for biologists, bioinformaticians, and software developers. Pathway data is available to view in our [Pathway Browser](</PathwayBrowser/>), to [analyze](</PathwayBrowser/#TOOL=AT>) your own dataset, to [download](</download-data>), and to access programmatically through our [Content](</ContentService/>) and [Analysis](</AnalysisService/>) Services. The [ReactomeFIViz app](</tools/reactome-fiviz>) for Cytoscape provides tools to find pathways and network patterns related to cancer and other types of diseases.
 
-**Documentation and Training**. Visit our online [User Guide](</userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
+**Documentation and Training**. Visit our online [User Guide](</documentation/userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</documentation/dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
 
 **About the Reactome Project**. Reactome is a collaboration between groups at the Ontario Institute for Cancer Research, Oregon Health and Science University, New York University Langone Medical Center, and The European Bioinformatics Institute. Reactome annotation files and interaction data derived from Reactome are distributed under a Creative Commons Public Domain (CC0 1.0 Universal) Licence. A Creative Commons Attribution 4.0 International (CC BY 4.0) Licence will apply to all software and code, database data dumps, and Pathway Illustrations (Enhanced High-Level Diagrams), Icon Library, Art and Branding Materials. A full description of the new and updated content is available on the Reactome [website](<https://reactome.org>).
 

projects/website-angular/content/about/news/145-version-71-releases.mdx

@@ -19,7 +19,7 @@ tags: ["about", "news", "145-version-71-releases"]
 
 **Tools and Data.** Our services and software tools are designed for biologists, bioinformaticians, and software developers. Pathway data is available to view in our [Pathway Browser](</PathwayBrowser/>), to [analyze](</PathwayBrowser/#TOOL=AT>) your own dataset, to [download](</download-data>), and to access programmatically through our [Content](</ContentService/>) and [Analysis](</AnalysisService/>) Services. The [ReactomeFIViz app](</tools/reactome-fiviz>) for Cytoscape provides tools to find pathways and network patterns related to cancer and other types of diseases.
 
-**Documentation and Training**. Visit our online [User Guide](</userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
+**Documentation and Training**. Visit our online [User Guide](</documentation/userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</documentation/dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
 
 **About the Reactome Project**. Reactome is a collaboration between groups at the Ontario Institute for Cancer Research, Oregon Health and Science University, New York University Langone Medical Center, and The European Bioinformatics Institute. Reactome annotation files and interaction data derived from Reactome are distributed under a Creative Commons Public Domain (CC0 1.0 Universal) Licence. A Creative Commons Attribution 4.0 International (CC BY 4.0) Licence will apply to all software and code, database data dumps, and Pathway Illustrations (Enhanced High-Level Diagrams), Icon Library, Art and Branding Materials. A full description of the new and updated content is available on the Reactome [website](<https:>).
 

projects/website-angular/content/about/news/147-version-72-released.mdx

@@ -19,7 +19,7 @@ tags: ["about", "news", "147-version-72-released"]
 
 **Tools and Data.** Our services and software tools are designed for biologists, bioinformaticians, and software developers. Pathway data is available to view in our [Pathway Browser](</PathwayBrowser/>), to [analyze](</PathwayBrowser/#TOOL=AT>) your own dataset, to [download](</download-data>), and to access programmatically through our [Content](</ContentService/>) and [Analysis](</AnalysisService/>) Services. The [ReactomeFIViz app](</tools/reactome-fiviz>) for Cytoscape provides tools to find pathways and network patterns related to cancer and other types of diseases.
 
-**Documentation and Training**. Visit our online [User Guide](</userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
+**Documentation and Training**. Visit our online [User Guide](</documentation/userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</documentation/dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
 
 **About the Reactome Project**. Reactome is a collaboration between groups at the Ontario Institute for Cancer Research, Oregon Health and Science University, New York University Langone Medical Center, and The European Bioinformatics Institute. Reactome annotation files and interaction data derived from Reactome are distributed under a Creative Commons Public Domain (CC0 1.0 Universal) Licence. A Creative Commons Attribution 4.0 International (CC BY 4.0) Licence will apply to all software and code, database data dumps, and Pathway Illustrations (Enhanced High-Level Diagrams), Icon Library, Art and Branding Materials. A full description of the new and updated content is available on the Reactome [website](<https:>).
 

projects/website-angular/content/about/news/151-new-package-facilitates-communication-between-reactome-services-and-data-with-python.mdx

@@ -13,4 +13,4 @@ Data science represents a new and evolving way of doing scientific research with
 
 Given the popularity of the Python programming language among data scientists, we have created the [reactome2py package](<https://reactome.github.io/reactome2py/>), which facilitates communication between our tools and web services with Python. The reactome2py package consists of a library of helper functions that wrap calls to the Reactome RESTful API and a utility module that simplifies access to our open-data.
 
-The [Pathway Analysis Service](</documentation/dev/analysis>) pathway over-representation and expression analysis as well as a species comparison tool. Further details regarding the AnalysisService API calls are available [here](</AnalysisService/>). The [Content Service](</documentation/dev/content-service>) provides access to our data via an easy [API](</ContentService/>) based on the Representational State Transfer (REST) protocol.  Finally, Utility ([Utils](<https://reactome.github.io/reactome2py/utils.html>)) provides functions for fetching pathway, drug, and drug-target data, other annotations, mapping information, and overlay data from human networks. Further details regarding the Data model key classes are available [here](</documentation/data-model>). Explore our tools and web services and learn how to include them in your applications at our [Developer's Zone](</dev>).
+The [Pathway Analysis Service](</documentation/dev/analysis>) pathway over-representation and expression analysis as well as a species comparison tool. Further details regarding the AnalysisService API calls are available [here](</AnalysisService/>). The [Content Service](</documentation/dev/content-service>) provides access to our data via an easy [API](</ContentService/>) based on the Representational State Transfer (REST) protocol.  Finally, Utility ([Utils](<https://reactome.github.io/reactome2py/utils.html>)) provides functions for fetching pathway, drug, and drug-target data, other annotations, mapping information, and overlay data from human networks. Further details regarding the Data model key classes are available [here](</documentation/data-model>). Explore our tools and web services and learn how to include them in your applications at our [Developer's Zone](</documentation/dev>).

projects/website-angular/content/about/news/155-version-73-released.mdx

@@ -21,7 +21,7 @@ tags: ["about", "news", "155-version-73-released"]
 
 **Tools and Data.** Our services and software tools are designed for biologists, bioinformaticians, and software developers. Pathway data is available to view in our [Pathway Browser](</PathwayBrowser/>), to [analyze](</PathwayBrowser/#TOOL=AT>) your own dataset, to [download](</download-data>), and to access programmatically through our [Content](</ContentService/>) and [Analysis](</AnalysisService/>) Services. The [ReactomeFIViz app](</tools/reactome-fiviz>) for Cytoscape provides tools to find pathways and network patterns related to cancer and other types of diseases.
 
-**Documentation and Training**. Visit our online [User Guide](</userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
+**Documentation and Training**. Visit our online [User Guide](</documentation/userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</documentation/dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
 
 **About the Reactome Project**. Reactome is a collaboration between groups at the Ontario Institute for Cancer Research, Oregon Health and Science University, New York University Langone Medical Center, and The European Bioinformatics Institute. Reactome annotation files and interaction data derived from Reactome are distributed under a Creative Commons Public Domain (CC0 1.0 Universal) Licence. A Creative Commons Attribution 4.0 International (CC BY 4.0) Licence will apply to all software and code, database data dumps, and Pathway Illustrations (Enhanced High-Level Diagrams), Icon Library, Art and Branding Materials. A full description of the new and updated content is available on the Reactome [website](<https:>).
 

projects/website-angular/content/about/news/161-version-74-released.mdx

@@ -21,7 +21,7 @@ tags: ["about", "news", "161-version-74-released"]
 
 **Tools and Data.** Our services and software tools are designed for biologists, bioinformaticians, and software developers. Pathway data is available to view in our [Pathway Browser](</PathwayBrowser/>), to [analyze](</PathwayBrowser/#TOOL=AT>) your own dataset, to [download](</download-data>), and to access programmatically through our [Content](</ContentService/>) and [Analysis](</AnalysisService/>) Services. The [ReactomeFIViz app](</tools/reactome-fiviz>) for Cytoscape provides tools to find pathways and network patterns related to cancer and other types of diseases.
 
-**Documentation and Training**. Visit our online [User Guide](</userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
+**Documentation and Training**. Visit our online [User Guide](</documentation/userguide>) to access documentation supporting pathway analysis of experimental data. The [Developer's Zone](</documentation/dev>) provides detailed documentation regarding our software, tools, and web services. Training and learning materials can be found [here](</community/training>).
 
 **About the Reactome Project**. Reactome is a collaboration between groups at the Ontario Institute for Cancer Research, Oregon Health and Science University, New York University Langone Medical Center, and The European Bioinformatics Institute. Reactome annotation files and interaction data derived from Reactome are distributed under a Creative Commons Public Domain (CC0 1.0 Universal) Licence. A Creative Commons Attribution 4.0 International (CC BY 4.0) Licence will apply to all software and code, database data dumps, and Pathway Illustrations (Enhanced High-Level Diagrams), Icon Library, Art and Branding Materials. A full description of the new and updated content is available on the Reactome [website](<https:>).