When Navidrome and the backend run in separate containers, Navidrome returns
absolute paths rooted at its own mount (e.g. /opt/navidrome/music) which
don't exist in the backend container (mounted at /music).
Add three-stage fallback:
1. _rebasePath: strip leading path components and try under CONFIG.musicPath
2. _findFileRecursive: exact filename search under CONFIG.musicPath
3. _findFileInDir: fuzzy search in album dir by track-number prefix or title stem
(handles files renamed to include artist in the filename)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>