* DOC-3388: Add getContent and setContent examples to save-content partial (#4052)

Add programmatic get/set content section with runnable examples
using editor.getContent(), getContent({ format: 'text' }), and
editor.setContent() to address Context7 benchmark Q3 (12/100).

* DOC-3389: Strengthen add-css-options page for custom content CSS (#4053)

Update description and add keywords for content_css and content_style.
Add intro paragraph explaining the two options to address Context7
benchmark Q8 (0/100).

* DOC-3390: Add editor.on('change') example to events page (#4054)

Add content change callback example using setup option and
editor.on('change') to address Context7 benchmark Q4 (30/100).

* DOC-3391: Add addButton and addCommand example to creating-a-plugin (#4055)

* DOC-3391: Add addButton and addCommand example to creating-a-plugin

Add toolbar button section showing PluginManager.add with
editor.ui.registry.addButton and editor.addCommand to address
Context7 benchmark Q9 (15/100).

* Update modules/ROOT/pages/creating-a-plugin.adoc

Co-authored-by: Millie <millie.macdonald@tiny.cloud>

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Co-authored-by: Millie <millie.macdonald@tiny.cloud>

* DOC-3392: Add programmatic mode.set example to readonly docs (#4056)

Add example showing editor.mode.set('readonly') and
editor.mode.set('design') for runtime mode switching to address
Context7 benchmark Q7 (25/100).

* DOC-3393: Add plugins and toolbar multi-plugin example to quickstart (#4057)

Add "Configure plugins and toolbar" section with plugins: 'image code'
and toolbar example to the quickstart partial to address Context7
benchmark Q2 (56/100).

* DOC-3394: Add content filtering intro to content-filtering page (#4058)

Update description and keywords to mention valid_elements,
invalid_elements, extended_valid_elements. Add intro paragraph
summarizing key filtering options to address Context7 benchmark
Q10 (22/100).

* DOC-3395: Improve quickstart keywords for selector/ID discoverability (#4059)

Add selector, textarea, id, tinymce.init keywords to all quickstart
pages (cloud, npm, php, .net, zip) to address Context7 benchmark
Q1 (62/100).

* DOC-3396: Improve custom-toolbarbuttons and file-image-upload metadata (#4060)

Update description and keywords for custom-toolbarbuttons (addButton,
custom button), file-image-upload (images_upload_handler), and
upload-images pages to address Context7 benchmark Q5/Q6 (25/100 each).

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Co-authored-by: Millie <millie.macdonald@tiny.cloud>