feat: 초기 커밋

- Progress Quest 6.4 Flutter 포팅 프로젝트
- 게임 루프, 상태 관리, UI 구현
- 캐릭터 생성, 인벤토리, 장비, 주문 시스템
- 시장/판매/구매 메커니즘

lib/src/core/engine/reward_service.dart

@@ -0,0 +1,26 @@
+import 'package:askiineverdie/src/core/engine/game_mutations.dart';
+import 'package:askiineverdie/src/core/model/equipment_slot.dart';
+import 'package:askiineverdie/src/core/model/game_state.dart';
+import 'package:askiineverdie/src/core/util/pq_logic.dart';
+
+/// Applies quest/act rewards to the GameState using shared RNG.
+class RewardService {
+  RewardService(this.mutations);
+
+  final GameMutations mutations;
+
+  GameState applyReward(GameState state, RewardKind reward) {
+    switch (reward) {
+      case RewardKind.spell:
+        return mutations.winSpell(state, state.stats.wis, state.traits.level);
+      case RewardKind.equip:
+        final slot = EquipmentSlot
+            .values[state.rng.nextInt(EquipmentSlot.values.length)];
+        return mutations.winEquip(state, state.traits.level, slot);
+      case RewardKind.stat:
+        return mutations.winStat(state);
+      case RewardKind.item:
+        return mutations.winItem(state);
+    }
+  }
+}