fix(server): GC test seeds tracks with file_size + file_format

Second go-round of the same shape of bug: tracks has file_size +
file_format NOT NULL (0002_core_library.up.sql) and my GC test seed
omitted both. The previous fix only addressed the artists.sort_name
column; the tracks INSERT was missing two more.

Use plausible stub values — the GC sweep only joins on track_id,
none of these columns affect what the test exercises.

internal/gc/worker_test.go

@@ -80,9 +80,14 @@ func TestGcCloseStalePlayEvents_ClosesOnly24hOldRows(t *testing.T) {
 	`, artistID).Scan(&albumID); err != nil {
 		t.Fatalf("seed album: %v", err)
 	}
+	// `tracks` has file_size + file_format NOT NULL. Use plausible
+	// stub values — the GC sweep doesn't read any of these columns,
+	// it only joins on track_id.
 	if err := pool.QueryRow(ctx, `
-		INSERT INTO tracks (album_id, artist_id, title, file_path, duration_ms)
-		VALUES ($1, $2, 'T', '/x.mp3', 180000) RETURNING id
+		INSERT INTO tracks (album_id, artist_id, title, file_path,
+		                    duration_ms, file_size, file_format)
+		VALUES ($1, $2, 'T', '/x.mp3', 180000, 4_000_000, 'mp3')
+		RETURNING id
 	`, albumID, artistID).Scan(&trackID); err != nil {
 		t.Fatalf("seed track: %v", err)
 	}