chore: 미사용 StoryService 인스턴스 제거 및 iOS 최소 버전 명시

- game_play_screen: 미사용 _storyService 인스턴스 및 import 제거
- iOS Podfile: platform :ios, '13.0' 명시

lib/src/features/game/game_play_screen.dart

@@ -9,7 +9,7 @@ import 'package:asciineverdie/src/core/model/treasure_chest.dart';
 import 'package:asciineverdie/data/story_data.dart';
 import 'package:asciineverdie/l10n/app_localizations.dart';
 import 'package:asciineverdie/src/shared/animation/ascii_animation_type.dart';
-import 'package:asciineverdie/src/core/engine/story_service.dart';
+
 import 'package:asciineverdie/src/core/model/game_state.dart';
 import 'package:asciineverdie/src/core/notification/notification_service.dart';
 import 'package:asciineverdie/src/features/game/game_session_controller.dart';
@@ -63,8 +63,7 @@ class _GamePlayScreenState extends State<GamePlayScreen>
   // Phase 8: 알림 서비스 (Notification Service)
   late final NotificationService _notificationService;
 
-  // Phase 9: 스토리 서비스 (Story Service)
-  late final StoryService _storyService;
+  // Phase 9: 스토리 Act 추적
   StoryAct _lastAct = StoryAct.prologue;
   bool _showingCinematic = false;
 
@@ -193,7 +192,6 @@ class _GamePlayScreenState extends State<GamePlayScreen>
   void initState() {
     super.initState();
     _notificationService = NotificationService();
-    _storyService = StoryService();
 
     // 오디오 컨트롤러 초기화
     _audioController = GameAudioController(
@@ -245,7 +243,6 @@ class _GamePlayScreenState extends State<GamePlayScreen>
   @override
   void dispose() {
     _notificationService.dispose();
-    _storyService.dispose();
     WidgetsBinding.instance.removeObserver(this);
     widget.controller.removeListener(_onControllerChanged);
     widget.controller.onReturnRewardAvailable = null; // Phase 7: 콜백 정리