feat: add skill-git banner and generate logo-full

- Set skill-git project cover image to assets/images/projects/skill-git-banner.png
- Add generated KnowledgeXLab logo-full.png (left icon + right calligraphic text)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jokester-zzz

_data/projects.yml

@@ -12,6 +12,6 @@
   status: "active"
   tags: ["AI Agent", "Claude Code", "Developer Tools"]
   cover_emoji: "🔧"
-  cover_image: ""
+  cover_image: "/assets/images/projects/skill-git-banner.png"
   url: "https://github.com/KnowledgeXLab/skill-git"
   papers: []