feat(death): 사망/부활 시스템 개선

- DeathInfo에 lostItem 필드 추가 (광고 부활 시 복구용)
- 세이브 데이터 v4: MonetizationState 포함
- 사망 오버레이 UI 개선
- 부활 서비스 광고 연동

lib/src/core/storage/save_manager.dart

@@ -1,4 +1,5 @@
 import 'package:asciineverdie/src/core/model/game_state.dart';
+import 'package:asciineverdie/src/core/model/monetization_state.dart';
 import 'package:asciineverdie/src/core/model/save_data.dart';
 import 'package:asciineverdie/src/core/storage/save_repository.dart';
 import 'package:asciineverdie/src/core/storage/save_service.dart'
@@ -13,23 +14,36 @@ class SaveManager {
 
   /// Save current game state to disk. [fileName] may be absolute or relative.
   /// Returns outcome with error on failure.
+  ///
+  /// [monetization] 저장 시 lastPlayTime을 현재 시간으로 자동 업데이트
   Future<SaveOutcome> saveState(
     GameState state, {
     String? fileName,
     bool cheatsEnabled = false,
+    MonetizationState? monetization,
   }) {
-    final save = GameSave.fromState(state, cheatsEnabled: cheatsEnabled);
+    // lastPlayTime을 현재 시간으로 업데이트
+    final updatedMonetization = (monetization ?? MonetizationState.initial())
+        .copyWith(lastPlayTime: DateTime.now());
+
+    final save = GameSave.fromState(
+      state,
+      cheatsEnabled: cheatsEnabled,
+      monetization: updatedMonetization,
+    );
     return _repo.save(save, fileName ?? defaultFileName);
   }
 
   /// Load game state from disk. [fileName] may be absolute (e.g., file picker).
-  /// Returns outcome + optional state + cheatsEnabled flag.
-  Future<(SaveOutcome, GameState?, bool)> loadState({String? fileName}) async {
+  /// Returns outcome + optional state + cheatsEnabled flag + monetization state.
+  Future<(SaveOutcome, GameState?, bool, MonetizationState?)> loadState({
+    String? fileName,
+  }) async {
     final (outcome, save) = await _repo.load(fileName ?? defaultFileName);
     if (!outcome.success || save == null) {
-      return (outcome, null, false);
+      return (outcome, null, false, null);
     }
-    return (outcome, save.toState(), save.cheatsEnabled);
+    return (outcome, save.toState(), save.cheatsEnabled, save.monetization);
   }
 
   /// 저장 파일 목록 조회