feat(metadata): implement single-track metadata editor API (§A7/§1H)

Adds inline AcoustID match-finding (multiple ranked candidates via
lookup_all) and PUT /tracks/{id}/metadata for manual edits, resolving
artist/album and setting metadata_status=manual. Extends TrackOut with
genre/year/track_number.

app/infrastructure/db/repositories/track_repository.py

@@ -26,6 +26,7 @@ def _to_entity(row: TrackModel) -> Track:
         duration_seconds=row.duration_seconds,
         genre=row.genre,
         year=row.year,
+        track_number=row.track_number,
         metadata_status=row.metadata_status,
         metadata_error=row.metadata_error,
         enriched_at=row.enriched_at,
@@ -162,6 +163,9 @@ class SqlAlchemyTrackRepository:
         title: str | None,
         genre: str | None,
         year: int | None,
+        artist_id: uuid.UUID | None = None,
+        album_id: uuid.UUID | None = None,
+        track_number: int | None = None,
     ) -> Track:
         row = await self._session.get(TrackModel, track_id)
         if row is None:
@@ -172,6 +176,12 @@ class SqlAlchemyTrackRepository:
             row.genre = genre
         if year is not None:
             row.year = year
+        if artist_id is not None:
+            row.artist_id = artist_id
+        if album_id is not None:
+            row.album_id = album_id
+        if track_number is not None:
+            row.track_number = track_number
         row.metadata_status = "manual"
         await self._session.flush()
         await self._session.refresh(row)