feat(ui): 사망 화면 잃은 아이템 희귀도 색상 표시

- DeathInfo에 lostItemRarity 필드 추가
- 사망 처리 시 아이템 희귀도 저장
- 사망 오버레이에서 희귀도별 색상 적용
  - Common: 회색, Uncommon: 녹색, Rare: 파랑
  - Epic: 보라, Legendary: 주황

lib/src/core/engine/progress_service.dart

@@ -16,6 +16,7 @@ import 'package:asciineverdie/src/core/model/combat_stats.dart';
 import 'package:asciineverdie/src/core/model/equipment_item.dart';
 import 'package:asciineverdie/src/core/model/equipment_slot.dart';
 import 'package:asciineverdie/src/core/model/game_state.dart';
+import 'package:asciineverdie/src/core/model/item_stats.dart';
 import 'package:asciineverdie/src/core/model/monster_combat_stats.dart';
 import 'package:asciineverdie/src/core/model/monster_grade.dart';
 import 'package:asciineverdie/src/core/model/potion.dart';
@@ -970,6 +971,7 @@ class ProgressService {
     var lostCount = 0;
     String? lostItemName;
     EquipmentSlot? lostItemSlot;
+    ItemRarity? lostItemRarity;
 
     if (!isBossDeath) {
       // 무기(슬롯 0)를 제외한 장착된 장비 중 1개를 제물로 삭제
@@ -999,6 +1001,7 @@ class ProgressService {
         final lostItem = state.equipment.getItemByIndex(sacrificeIndex);
         lostItemName = lostItem.name;
         lostItemSlot = EquipmentSlot.values[sacrificeIndex];
+        lostItemRarity = lostItem.rarity;
 
         // 해당 슬롯을 빈 장비로 교체
         newEquipment = newEquipment.setItemByIndex(
@@ -1015,6 +1018,7 @@ class ProgressService {
       lostEquipmentCount: lostCount,
       lostItemName: lostItemName,
       lostItemSlot: lostItemSlot,
+      lostItemRarity: lostItemRarity,
       goldAtDeath: state.inventory.gold,
       levelAtDeath: state.traits.level,
       timestamp: state.skillSystem.elapsedMs,