perf(smartplaylist): batch-load genres instead of per-row correlated subquery

Evaluate now issues a lean main SELECT over the joined metadata tables
with no genre column, then batch-fetches genres with a single query
using WHERE recording_id IN (...). Previously the track_metadata view's
correlated GROUP_CONCAT subquery ran per row and scaled with library
size rather than result size, producing multi-second load times for
100-track smart playlists.

- Inline the metadata joins instead of using the track_metadata view,
  so the per-row GROUP_CONCAT never runs on the hot path. Other
  callers of the view (search, library listing) are unaffected.
- Route all genre operators (is/is_not/is_any_of/contains/etc.)
  through a recording_genres subquery against af.recording_id.
  Previously text operators like "contains" matched against the
  view's concatenated genre column, which is no longer in scope.
- Sort-by-genre falls back to Go-side sort after the batch genre
  merge since there is no single SQL column to sort on.
- Log main_ms / genres_ms / total_ms at Debug for future tuning.
- Add (*DB).Logger() accessor so smartplaylist can reuse the DB's
  structured logger without changing Evaluate's signature.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/database/database.go

@@ -148,6 +148,12 @@ func (d *DB) QueryContext(query string, args ...any) (*sql.Rows, error) {
 	return d.db.QueryContext(d.Ctx, query, args...)
 }
 
+// Logger returns the structured logger bound to this DB. Callers can
+// use it to emit timing or diagnostic logs from query-adjacent code.
+func (d *DB) Logger() *slog.Logger {
+	return d.logger
+}
+
 // applyPRAGMAs configures SQLite connection settings. Called by both
 // NewDB and NewTestDB to ensure identical behavior.
 func applyPRAGMAs(ctx context.Context, db *sql.DB) error {
@@ -1222,7 +1228,7 @@ func migration9SmartPlaylists(
 // migration10PlayHistory adds play history tracking:
 // - play_history table for timestamped play log
 // - play_count and last_played columns on audio_files
-// - Recreates track_metadata VIEW to expose the new columns
+// - Recreates track_metadata VIEW to expose the new columns.
 func migration10PlayHistory(
 	ctx context.Context,
 	db *sql.DB,