feat(docs): enhance documentation UI with ToC and GitHub stats

Add new features to documentation UI:
- Add table of contents with scroll spy functionality
- Add GitHub repository statistics badge
- Implement new centered layout system with fixed sidebar
- Add conditional Playwright installation based on CRAWL4AI_MODE

Breaking changes: None

mkdocs.yml

@@ -76,6 +76,7 @@ extra:
   version: !ENV [CRAWL4AI_VERSION, 'development']
 
 extra_css:
+  - assets/layout.css
   - assets/styles.css
   - assets/highlight.css
   - assets/dmvendor.css
@@ -83,4 +84,6 @@ extra_css:
 extra_javascript:
   - assets/highlight.min.js
   - assets/highlight_init.js
-  - https://buttons.github.io/buttons.js
+  - https://buttons.github.io/buttons.js
+  - assets/toc.js
+  - assets/github_stats.js