fix: show album artist on featured compilation cards (#979)

* fix: show album artist on featured compilation cards

The 'Also featured on' cards are synthesised from search3 child songs,
which only read the flat `albumArtist` field. Compilation children leave
that empty — the album-artist credit lives in OpenSubsonic's structured
`albumArtists` / `displayAlbumArtist` — so the card fell back to the '—'
placeholder. Carry the structured credit (and the display string) onto
the synthesised album so it resolves a name (and stays navigable when the
server supplies an id).

* docs: changelog for featured-compilation artist credit (#979)

src/api/subsonicTypes.ts

@@ -72,6 +72,8 @@ export interface SubsonicSong {
   genre?: string;
   path?: string;
   albumArtist?: string;
+  /** OpenSubsonic: single-string album-artist for display (mirrors `albumArtists` joined). */
+  displayAlbumArtist?: string;
   /** ISRC code when available (e.g., Navidrome) */
   isrc?: string;
   /** Times the track has been played, surfaced by Navidrome's Subsonic API. */