feat(db): cascade-cleanup queries for M7 #372 track removal

DeleteTrack returns album_id + artist_id so the calling service can
chain the album-empty / artist-empty cascade. DeleteAlbumIfEmpty and
DeleteArtistIfEmpty are no-ops when other rows still reference the
parent — the service treats pgx.ErrNoRows as "not orphaned, skip".

internal/db/queries/tracks.sql

@@ -96,3 +96,12 @@ ORDER BY albums.release_date NULLS LAST, albums.sort_title,
 -- matched artist (sum across all the artist's albums) while a request
 -- is still in flight.
 SELECT COUNT(*) FROM tracks WHERE artist_id = $1;
+
+-- name: DeleteTrack :one
+-- M7 #372: hard delete with FK cascade. The CASCADE on track_id from
+-- play_events / general_likes_tracks / lidarr_quarantine /
+-- lidarr_quarantine_actions handles their cleanup. RETURNING gives us
+-- album_id + artist_id for the album-empty / artist-empty cascade
+-- checks the service does next.
+DELETE FROM tracks WHERE id = $1
+RETURNING id, album_id, artist_id, file_path, mbid;