SpotifyBU 1.6.0

SpotifyBU 1.6.0

SpotifyBU 1.6.0 adds durable Spotify identity tagging for SpotifyBU-managed
downloads, so newly tagged files can reconnect to Spotify tracks even after
another organizer moves or renames them.

Added

• SpotifyBU provider downloads now write custom Spotify identity metadata:
  spotifybu:track_id, spotifybu:track_uri, spotifybu:album_id,
  spotifybu:isrc, and spotifybu:identity_version.
• Library indexing reads those identity tags into optional indexed-track fields
  while preserving compatibility with existing .spotifybu/library-index.json
  files.
• Music library matching now checks exact Spotify track ID and URI matches
  before falling back to ISRC, metadata, duration, and path matching.
• Settings includes a maintenance action to retag already matched backups from
  saved SpotifyBU playlist snapshots.
• A new /api/music-library/identity-tags endpoint runs the backfill workflow.

Changed

• SpotifyBU-created files keep normal title, artist, album, album artist, track,
  disc, and ISRC tags unchanged while adding the durable identity tags.
• Playlist membership remains in SpotifyBU's playlist backup snapshots and local
  database, not in audio-file metadata.

Verified

• TypeScript check passes with tsc --noEmit.
• Production build passes with next build.
• Unit tests pass with npm test.