New repair job that scans the library for tracks filed under "Unknown
Artist" and corrects them. Resolves correct metadata by:
1. Reading embedded file tags (if file has correct artist)
2. Looking up by source track ID (Spotify/Deezer/iTunes)
3. Searching by title as last resort
Dry run mode (default) creates findings for review. Live mode re-tags
the audio file, moves it to the correct folder structure, and updates
the database. Includes fix handler for applying individual findings.
