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/albums.sql

@@ -85,3 +85,14 @@ SELECT COUNT(*) FROM albums;
 -- Used by request-progress reporting to count how many albums have been
 -- ingested for a matched artist while a request is still in flight.
 SELECT COUNT(*) FROM albums WHERE artist_id = $1;
+
+-- name: DeleteAlbumIfEmpty :one
+-- M7 #372: deletes the album row only when it has no remaining tracks.
+-- Used after a track delete to tidy up orphaned albums. RETURNING gives
+-- us the artist_id so the service can chain into the artist-empty check.
+-- Returns no rows when the album still has tracks; the service treats
+-- pgx.ErrNoRows as "album not orphaned, skip cascade".
+DELETE FROM albums a
+WHERE a.id = $1
+  AND NOT EXISTS (SELECT 1 FROM tracks t WHERE t.album_id = a.id)
+RETURNING a.id, a.artist_id;

internal/db/queries/artists.sql

@@ -64,3 +64,13 @@ LEFT JOIN LATERAL (
 ) cnt ON true
 ORDER BY artists.sort_name, artists.name, artists.id
 LIMIT $1 OFFSET $2;
+
+-- name: DeleteArtistIfEmpty :one
+-- M7 #372: deletes the artist row only when it has no remaining albums
+-- AND no remaining tracks (defensive — tracks can in principle exist
+-- without an album, though the scanner doesn't write that shape today).
+DELETE FROM artists a
+WHERE a.id = $1
+  AND NOT EXISTS (SELECT 1 FROM albums al WHERE al.artist_id = a.id)
+  AND NOT EXISTS (SELECT 1 FROM tracks t WHERE t.artist_id = a.id)
+RETURNING a.id;

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;