perf(app): 초기화 병렬 처리 및 UI 개선

## 성능 최적화

### main.dart
- 앱 초기화 병렬 처리 (Future.wait 활용)
- 광고 SDK, Hive 초기화 동시 실행
- Hive Box 오픈 병렬 처리
- 코드 구조화 (_initializeHive, _initializeNotifications)

### visit_provider.dart
- allLastVisitDatesProvider 추가
- 리스트 화면에서 N+1 쿼리 방지
- 모든 맛집의 마지막 방문일 일괄 조회

## UI 개선

### 각 화면 리팩토링
- AppDimensions 상수 적용
- 스켈레톤 로더 적용
- 코드 정리 및 일관성 개선

lib/main.dart

@@ -22,14 +22,28 @@ import 'data/sample/sample_data_initializer.dart';
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
 
-  if (AdHelper.isMobilePlatform) {
-    await MobileAds.instance.initialize();
-  }
-
-  // Initialize timezone
+  // Initialize timezone (동기, 빠름)
   tz.initializeTimeZones();
 
-  // Initialize Hive
+  // 광고 SDK와 Hive 초기화를 병렬 처리
+  await Future.wait([
+    if (AdHelper.isMobilePlatform) MobileAds.instance.initialize(),
+    _initializeHive(),
+  ]);
+
+  // Hive 초기화 후 병렬 처리 가능한 작업들
+  await Future.wait([
+    SampleDataInitializer.seedInitialData(),
+    _initializeNotifications(),
+    AdaptiveTheme.getThemeMode(),
+  ]).then((results) {
+    final savedThemeMode = results[2] as AdaptiveThemeMode?;
+    runApp(ProviderScope(child: LunchPickApp(savedThemeMode: savedThemeMode)));
+  });
+}
+
+/// Hive 초기화 및 Box 오픈
+Future<void> _initializeHive() async {
   await Hive.initFlutter();
 
   // Register Hive Adapters
@@ -39,24 +53,21 @@ void main() async {
   Hive.registerAdapter(RecommendationRecordAdapter());
   Hive.registerAdapter(UserSettingsAdapter());
 
-  // Open Hive Boxes
-  await Hive.openBox<Restaurant>(AppConstants.restaurantBox);
-  await Hive.openBox<VisitRecord>(AppConstants.visitRecordBox);
-  await Hive.openBox<RecommendationRecord>(AppConstants.recommendationBox);
-  await Hive.openBox(AppConstants.settingsBox);
-  await Hive.openBox<UserSettings>('user_settings');
-  await SampleDataInitializer.seedInitialData();
+  // Open Hive Boxes (병렬 오픈)
+  await Future.wait([
+    Hive.openBox<Restaurant>(AppConstants.restaurantBox),
+    Hive.openBox<VisitRecord>(AppConstants.visitRecordBox),
+    Hive.openBox<RecommendationRecord>(AppConstants.recommendationBox),
+    Hive.openBox(AppConstants.settingsBox),
+    Hive.openBox<UserSettings>('user_settings'),
+  ]);
+}
 
-  // Initialize Notification Service (only for non-web platforms)
-  if (!kIsWeb) {
-    final notificationService = NotificationService();
-    await notificationService.ensureInitialized(requestPermission: true);
-  }
-
-  // Get saved theme mode
-  final savedThemeMode = await AdaptiveTheme.getThemeMode();
-
-  runApp(ProviderScope(child: LunchPickApp(savedThemeMode: savedThemeMode)));
+/// 알림 서비스 초기화 (비-웹 플랫폼)
+Future<void> _initializeNotifications() async {
+  if (kIsWeb) return;
+  final notificationService = NotificationService();
+  await notificationService.ensureInitialized(requestPermission: true);
 }
 
 class LunchPickApp extends StatelessWidget {