fix: clearing a wrong slot's MBID clears its source too, as tracks_mbid_source_pair requires (M498)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/dbq/tracks.sql.go

@@ -58,7 +58,7 @@ func (q *Queries) ClearStaleSuspectSourceTracks(ctx context.Context, pattern str
 
 const clearTrackMbids = `-- name: ClearTrackMbids :exec
 UPDATE tracks
-   SET mbid = NULL
+   SET mbid = NULL, mbid_source = NULL
  WHERE id = ANY($1::uuid[])
 `
 
@@ -66,6 +66,7 @@ UPDATE tracks
 // wrong-slot removal). The MBID came from that file, so it names the song kept
 // elsewhere on the album, and missing-pair folding would fold the emptied slot
 // into it: twelve slots went that way on 2026-10-20 and were never wanted back.
+// mbid_source goes with it (tracks_mbid_source_pair).
 func (q *Queries) ClearTrackMbids(ctx context.Context, ids []pgtype.UUID) error {
 	_, err := q.db.Exec(ctx, clearTrackMbids, ids)
 	return err