feat(server/m7-379): heal existing artist+album mbid on rescan

internal/db/dbq/albums.sql.go

@@ -515,6 +515,25 @@ func (q *Queries) SearchAlbums(ctx context.Context, arg SearchAlbumsParams) ([]A
 	return items, nil
 }
 
+const setAlbumMbidIfNull = `-- name: SetAlbumMbidIfNull :exec
+UPDATE albums
+   SET mbid = $2,
+       updated_at = now()
+ WHERE id = $1 AND mbid IS NULL
+`
+
+type SetAlbumMbidIfNullParams struct {
+	ID   pgtype.UUID
+	Mbid *string
+}
+
+// M7 #379: heal MBID on existing album rows during rescan. Idempotent —
+// only updates when the existing mbid is NULL.
+func (q *Queries) SetAlbumMbidIfNull(ctx context.Context, arg SetAlbumMbidIfNullParams) error {
+	_, err := q.db.Exec(ctx, setAlbumMbidIfNull, arg.ID, arg.Mbid)
+	return err
+}
+
 const upsertAlbum = `-- name: UpsertAlbum :one
 INSERT INTO albums (title, sort_title, artist_id, release_date, mbid, cover_art_path)
 VALUES ($1, $2, $3, $4, $5, $6)