fix(core): 오디오 및 진행 루프 수정

- AudioService 디버그 로그 정리
- ProgressLoop 개선

lib/src/core/audio/audio_service.dart

@@ -211,7 +211,6 @@ class AudioService {
     if (_currentBgm == name) return;
     if (_staticBgmPlayer == null) return;
 
-    debugPrint('[AudioService] playBgm requested: $name');
     await _playBgmInternal(name);
   }
 

lib/src/core/engine/progress_loop.dart

@@ -42,12 +42,14 @@ class ProgressLoop {
     this.onPlayerDied,
     this.onGameComplete,
     List<int> availableSpeeds = const [1, 5],
+    int initialSpeedMultiplier = 1,
   }) : _state = initialState,
        _tickInterval = tickInterval,
        _autoSaveConfig = autoSaveConfig,
        _now = now ?? DateTime.now,
        _stateController = StreamController<GameState>.broadcast(),
-       _availableSpeeds = availableSpeeds.isNotEmpty ? availableSpeeds : [1];
+       _availableSpeeds = availableSpeeds.isNotEmpty ? availableSpeeds : [1],
+       _speedMultiplier = initialSpeedMultiplier;
 
   final ProgressService progressService;
   final SaveManager? saveManager;
@@ -65,7 +67,7 @@ class ProgressLoop {
 
   Timer? _timer;
   int? _lastTickMs;
-  int _speedMultiplier = 1;
+  int _speedMultiplier;
   List<int> _availableSpeeds;
 
   GameState get current => _state;