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/model/save_data.dart

@@ -2,6 +2,7 @@ import 'dart:collection';
 
 import 'package:asciineverdie/src/core/model/equipment_item.dart';
 import 'package:asciineverdie/src/core/model/equipment_slot.dart';
+import 'package:asciineverdie/src/core/model/monetization_state.dart';
 import 'package:asciineverdie/src/core/model/monster_grade.dart';
 import 'package:asciineverdie/src/core/util/deterministic_random.dart';
 import 'package:asciineverdie/src/core/model/game_state.dart';
@@ -9,7 +10,8 @@ import 'package:asciineverdie/src/core/model/game_state.dart';
 /// 세이브 파일 버전
 /// - v2: 장비 이름만 저장 (레거시)
 /// - v3: 장비 전체 정보 저장 (level, rarity, stats 포함)
-const int kSaveVersion = 3;
+/// - v4: MonetizationState 추가, DeathInfo.lostItem 추가
+const int kSaveVersion = 4;
 
 class GameSave {
   GameSave({
@@ -23,9 +25,14 @@ class GameSave {
     required this.progress,
     required this.queue,
     this.cheatsEnabled = false,
+    this.monetization,
   });
 
-  factory GameSave.fromState(GameState state, {bool cheatsEnabled = false}) {
+  factory GameSave.fromState(
+    GameState state, {
+    bool cheatsEnabled = false,
+    MonetizationState? monetization,
+  }) {
     return GameSave(
       version: kSaveVersion,
       rngState: state.rng.state,
@@ -37,6 +44,7 @@ class GameSave {
       progress: state.progress,
       queue: state.queue,
       cheatsEnabled: cheatsEnabled,
+      monetization: monetization,
     );
   }
 
@@ -51,6 +59,9 @@ class GameSave {
   final QueueState queue;
   final bool cheatsEnabled;
 
+  /// 수익화 시스템 상태 (v4+)
+  final MonetizationState? monetization;
+
   Map<String, dynamic> toJson() {
     return {
       'version': version,
@@ -132,6 +143,7 @@ class GameSave {
             },
           )
           .toList(),
+      if (monetization != null) 'monetization': monetization!.toJson(),
     };
   }
 
@@ -244,6 +256,9 @@ class GameSave {
           }),
         ),
       ),
+      monetization: _monetizationFromJson(
+        json['monetization'] as Map<String, dynamic>?,
+      ),
     );
   }
 
@@ -355,3 +370,12 @@ Equipment _equipmentFromJson(Map<String, dynamic> json, int version) {
     bestIndex: json['bestIndex'] as int? ?? 0,
   );
 }
+
+/// MonetizationState 역직렬화 (v4+ 마이그레이션)
+///
+/// - v3 이하: null (기본값 사용)
+/// - v4 이상: 저장된 상태 로드
+MonetizationState? _monetizationFromJson(Map<String, dynamic>? json) {
+  if (json == null) return null;
+  return MonetizationState.fromJson(json);
+}