- Split renderer.js into 9 manager classes following SOLID principles:
* AppState - State management
* EpisodeManager - Episode numbering and range editing
* TagManager - File tagging system
* SearchManager - TheTVDB search integration
* FileManager - Directory and file operations
* ModalManager - Video preview modals
* ProgressManager - Progress display
* FileListManager - File list rendering and drag/drop
* UIManager - Main UI coordinator
- Add comprehensive test suite (test-renderer-classes-comprehensive.js)
with 100+ tests covering all business logic
- Fix drag/drop handler 'this' binding issues
- Add CSS for highlighted episodes and improved file list styling
- Restore all original functionality including episode cascading,
tagging system, TVDB search, and Jellyfin naming
