feat(core): 장비 시스템 및 게임 상태 모델 확장

- Equipment 클래스를 11개 슬롯으로 확장 (원본 Main.dfm 충실)
- TaskInfo에 몬스터 정보(baseName, part) 추가
- Stats에 현재 HP/MP 필드 추가
- 히스토리 기능 구현 (plotHistory, questHistory)
- pq_logic winEquip/winStatIndex 원본 로직 개선
- 퀘스트 몬스터 처리 로직 구현
- SaveData 직렬화 확장

lib/src/core/engine/reward_service.dart

@@ -1,5 +1,4 @@
 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';
 
@@ -14,9 +13,9 @@ class RewardService {
       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);
+        // 원본 Main.pas:797 - Random(Equips.Items.Count) (11개 슬롯)
+        final slotIndex = state.rng.nextInt(Equipment.slotCount);
+        return mutations.winEquipByIndex(state, state.traits.level, slotIndex);
       case RewardKind.stat:
         return mutations.winStat(state);
       case RewardKind.item: