feat: add ISRC matching for similar songs (#4946)

* feat: add ISRC support to similar songs matching and plugin interface

Add ISRC (International Standard Recording Code) as a high-priority
identifier in the provider matching algorithm, alongside MBID. The
matching pipeline now uses four strategies in priority order:
ID > MBID > ISRC > Title+Artist fuzzy match.

- Add ISRC field to agents.Song struct
- Add ISRC field to plugin capability SongRef (Go, Rust PDKs)
- Add loadTracksByISRC using json_tree query on tags column
- Integrate ISRC into matchSongsToLibrary, selectBestMatchingSongs,
  and buildTitleQueries

https://claude.ai/code/session_01Dd4mTq1VQZag4RNjCVusiF

* chore: regenerate plugin schema after ISRC addition

Run `make gen` to update the generated YAML schema for the
metadata agent capability with the new ISRC field on SongRef.

https://claude.ai/code/session_01Dd4mTq1VQZag4RNjCVusiF

* feat(mediafile): add GetAllByTags method to MediaFileRepository for tag-based retrieval

Signed-off-by: Deluan <deluan@navidrome.org>

* feat(provider): speed up track matching by incorporating prior matches in ISRC and MBID lookups

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Claude <noreply@anthropic.com>

plugins/pdk/go/metadata/metadata.go

@@ -171,6 +171,8 @@ type SongRef struct {
 	Name string `json:"name"`
 	// MBID is the MusicBrainz ID for the song.
 	MBID string `json:"mbid,omitempty"`
+	// ISRC is the International Standard Recording Code for the song.
+	ISRC string `json:"isrc,omitempty"`
 	// Artist is the artist name.
 	Artist string `json:"artist,omitempty"`
 	// ArtistMBID is the MusicBrainz artist ID.