fix artist refreshstats query

Signed-off-by: Deluan <deluan@navidrome.org>

cmd/scan.go

@@ -63,6 +63,8 @@ func trackScanAsSubprocess(ctx context.Context, progress <-chan *scanner.Progres
 }
 
 func runScanner(ctx context.Context) {
+	defer db.Init(ctx)()
+
 	sqlDB := db.Db()
 	defer db.Db().Close()
 	ds := persistence.New(sqlDB)

db/migrations/20251101180108_add_media_file_artists_artist_id_index.sql

@@ -0,0 +1,7 @@
+-- +goose Up
+-- Add index on artist_id for media_file_artists table to improve query performance
+-- This index is crucial for the RefreshStats query in artistRepository
+CREATE INDEX IF NOT EXISTS media_file_artists_artist_id ON media_file_artists(artist_id);
+
+-- +goose Down
+DROP INDEX IF EXISTS media_file_artists_artist_id;

persistence/artist_repository.go

@@ -399,7 +399,7 @@ func (r *artistRepository) RefreshStats(allArtists bool) (int64, error) {
 	}
 
 	// Template for the batch update with placeholder markers that we'll replace
-	// This now calculates per-library statistics and stores them in library_artist.stats
+	// This calculates per-library statistics and stores them in library_artist.stats
 	batchUpdateStatsSQL := `
     WITH artist_role_counters AS (
         SELECT mfa.artist_id,