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/capabilities/metadata_agent.go

@@ -142,6 +142,8 @@ 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.

plugins/capabilities/metadata_agent.yaml

@@ -343,6 +343,9 @@ components:
                 mbid:
                     type: string
                     description: MBID is the MusicBrainz ID for the song.
+                isrc:
+                    type: string
+                    description: ISRC is the International Standard Recording Code for the song.
                 artist:
                     type: string
                     description: Artist is the artist name.

plugins/metadata_agent.go

@@ -230,6 +230,7 @@ func songRefsToAgentSongs(refs []capabilities.SongRef) []agents.Song {
 			ID:         s.ID,
 			Name:       s.Name,
 			MBID:       s.MBID,
+			ISRC:       s.ISRC,
 			Artist:     s.Artist,
 			ArtistMBID: s.ArtistMBID,
 			Album:      s.Album,

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.

plugins/pdk/go/metadata/metadata_stub.go

@@ -168,6 +168,8 @@ 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.

plugins/pdk/rust/nd-pdk-capabilities/src/metadata.rs

@@ -242,6 +242,9 @@ pub struct SongRef {
     /// MBID is the MusicBrainz ID for the song.
     #[serde(default, skip_serializing_if = "String::is_empty")]
     pub mbid: String,
+    /// ISRC is the International Standard Recording Code for the song.
+    #[serde(default, skip_serializing_if = "String::is_empty")]
+    pub isrc: String,
     /// Artist is the artist name.
     #[serde(default, skip_serializing_if = "String::is_empty")]
     pub artist: String,

plugins/testdata/test-metadata-agent/main.go

@@ -134,6 +134,7 @@ func (t *testMetadataAgent) GetSimilarSongsByTrack(input metadata.SimilarSongsBy
 			ID:         "similar-track-id-" + strconv.Itoa(i+1),
 			Name:       "Similar to " + input.Name + " #" + strconv.Itoa(i+1),
 			MBID:       "similar-mbid-" + strconv.Itoa(i+1),
+			ISRC:       "similar-isrc-" + strconv.Itoa(i+1),
 			Artist:     input.Artist,
 			ArtistMBID: "artist-mbid-" + strconv.Itoa(i+1),
 		})