feat(app): add manual entry and sharing flows

lib/data/sample/sample_data_initializer.dart

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+import 'package:hive_flutter/hive_flutter.dart';
+import 'package:lunchpick/core/constants/app_constants.dart';
+import 'package:lunchpick/domain/entities/restaurant.dart';
+import 'package:lunchpick/domain/entities/visit_record.dart';
+
+import 'manual_restaurant_samples.dart';
+
+/// 초기 구동 시 샘플 데이터를 채워 넣는 도우미
+class SampleDataInitializer {
+  static Future<void> seedManualRestaurantsIfNeeded() async {
+    final restaurantBox = Hive.box<Restaurant>(AppConstants.restaurantBox);
+    final visitBox = Hive.box<VisitRecord>(AppConstants.visitRecordBox);
+
+    // 이미 사용자 데이터가 있으면 샘플을 추가하지 않음
+    if (restaurantBox.isNotEmpty || visitBox.isNotEmpty) {
+      return;
+    }
+
+    final samples = ManualRestaurantSamples.build();
+    for (final sample in samples) {
+      await restaurantBox.put(sample.restaurant.id, sample.restaurant);
+      for (final visit in sample.visits) {
+        await visitBox.put(visit.id, visit);
+      }
+    }
+  }
+}