Add media browser feature with UI improvements

- Refactored index.html: Split into separate HTML (309 lines), CSS (908 lines), and JS (1,286 lines) files
- Implemented media browser with folder configuration, recursive navigation, and thumbnail display
- Added metadata extraction using mutagen library (title, artist, album, duration, bitrate, codec)
- Implemented thumbnail generation and caching with SHA256 hash-based keys and LRU eviction
- Added platform-specific file playback (os.startfile on Windows, xdg-open on Linux, open on macOS)
- Implemented path validation security to prevent directory traversal attacks
- Added smooth thumbnail loading with fade-in animation and loading spinner
- Added i18n support for browser (English and Russian)
- Updated dependencies: mutagen>=1.47.0, pillow>=10.0.0
- Added comprehensive media browser documentation to README

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -75,6 +75,8 @@ Unregister-ScheduledTask -TaskName "MediaServer" -Confirm:$false
 
 **Best Practice:** Always restart the server immediately after committing backend changes to verify they work correctly before pushing.
 
+**CRITICAL** Always check acccessibility of WebUI after server restart to ensure that server has started without issues
+
 ## Configuration
 
 Copy `config.example.yaml` to `config.yaml` and customize.