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,

lib/src/core/model/game_state.dart

@@ -132,6 +132,7 @@ class DeathInfo {
     required this.timestamp,
     this.lostItemName,
     this.lostItemSlot,
+    this.lostItemRarity,
     this.lastCombatEvents = const [],
   });
 
@@ -150,6 +151,9 @@ class DeathInfo {
   /// 제물로 바친 아이템 슬롯 (null이면 없음)
   final EquipmentSlot? lostItemSlot;
 
+  /// 제물로 바친 아이템 희귀도 (null이면 없음)
+  final ItemRarity? lostItemRarity;
+
   /// 사망 시점 골드
   final int goldAtDeath;
 
@@ -168,6 +172,7 @@ class DeathInfo {
     int? lostEquipmentCount,
     String? lostItemName,
     EquipmentSlot? lostItemSlot,
+    ItemRarity? lostItemRarity,
     int? goldAtDeath,
     int? levelAtDeath,
     int? timestamp,
@@ -179,6 +184,7 @@ class DeathInfo {
       lostEquipmentCount: lostEquipmentCount ?? this.lostEquipmentCount,
       lostItemName: lostItemName ?? this.lostItemName,
       lostItemSlot: lostItemSlot ?? this.lostItemSlot,
+      lostItemRarity: lostItemRarity ?? this.lostItemRarity,
       goldAtDeath: goldAtDeath ?? this.goldAtDeath,
       levelAtDeath: levelAtDeath ?? this.levelAtDeath,
       timestamp: timestamp ?? this.timestamp,