phsl / new-api

- Fix thinking content area scroll functionality in MessageContent.js
  * Replace max-h-50 with explicit maxHeight style (200px)
  * Add thinking-content-scroll CSS class for proper scrollbar styling
  * Ensure scrollbars are visible when content exceeds container height
- Add thinking-content-scroll CSS class in index.css
  * Define webkit scrollbar styles with proper dimensions (6px)
  * Add hover effects and cross-browser compatibility
  * Support both webkit and Firefox scrollbar styling
- Remove unused CSS classes to improve code cleanliness
  * Remove .hide-on-mobile class (no usage found in codebase)
  * Remove .debug-code class (no longer needed)
- Improve user experience for viewing lengthy thinking content
  * Users can now properly scroll through AI reasoning content
  * Maintains content visibility with appropriate height constraints

Resolves issue where thinking section had max height but no scrolling capability.