feat(phase-13): implement recent files tracking system

Add recent files store for tracking recently opened/saved projects.

Features:
- Recent files store with persistence
- Track up to 10 recent files (configurable)
- Store file metadata:
  * Unique ID
  * File name
  * File path
  * Timestamp
  * Optional thumbnail
- Automatic duplicate removal (by path)
- Most recent files appear first
- Functions for managing recent files:
  * addRecentFile() - Add to recent list
  * removeRecentFile() - Remove specific file
  * clearRecentFiles() - Clear all recent
  * updateThumbnail() - Update file thumbnail
- localStorage persistence

Changes:
- Created store/recent-files-store.ts with RecentFile interface
- Exported from store/index.ts
- Ready for UI integration in File menu

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

store/index.ts

@@ -12,3 +12,4 @@ export * from './ui-store';
 export * from './toast-store';
 export * from './context-menu-store';
 export * from './guides-store';
+export * from './recent-files-store';