changed genre scanning to parse multiple genres, updated db to accommodate.

backend/database/sql/schemas/playlist_tracks.sql

@@ -6,3 +6,9 @@ CREATE TABLE IF NOT EXISTS playlist_tracks (
     FOREIGN KEY(playlist_id) REFERENCES playlists(id) ON DELETE CASCADE,
     FOREIGN KEY(audio_file_id) REFERENCES audio_files(id) ON DELETE CASCADE
 );
+
+CREATE INDEX IF NOT EXISTS idx_playlist_tracks_playlist_id
+    ON playlist_tracks(playlist_id);
+
+CREATE INDEX IF NOT EXISTS idx_playlist_tracks_audio_file_id
+    ON playlist_tracks(audio_file_id);