Add household sharing feature

✨ Features:
- Create household with 6-character shareable code
- Join existing household with code
- View household members and owner
- Leave household functionality
- Automatic inventory filtering by household
- Persistent household settings across app updates

🔧 Technical changes:
- Added Household model with Hive adapter (typeId: 4)
- Updated AppSettings with userName and currentHouseholdId fields
- Modified InventoryRepository to filter items by household
- Updated Add Item screen to set householdId on new items
- Added HouseholdScreen with full CRUD operations
- Integrated household sharing into Settings navigation

🎯 Behavior:
- Users not in a household see only their personal items
- Users in a household see shared household items
- New items automatically tagged with current household

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/data/local/hive_database.dart

@@ -1,6 +1,7 @@
 import 'package:hive_flutter/hive_flutter.dart';
 import '../../features/inventory/models/food_item.dart';
 import '../../features/settings/models/app_settings.dart';
+import '../../features/settings/models/household.dart';
 
 /// Singleton class to manage Hive database
 class HiveDatabase {
@@ -17,6 +18,7 @@ class HiveDatabase {
     Hive.registerAdapter(LocationAdapter());
     Hive.registerAdapter(ExpirationStatusAdapter());
     Hive.registerAdapter(AppSettingsAdapter());
+    Hive.registerAdapter(HouseholdAdapter());
 
     _initialized = true;
   }
@@ -48,6 +50,29 @@ class HiveDatabase {
     return box.getAt(0)!;
   }
 
+  /// Get the households box
+  static Future<Box<Household>> getHouseholdsBox() async {
+    if (!Hive.isBoxOpen('households')) {
+      return await Hive.openBox<Household>('households');
+    }
+    return Hive.box<Household>('households');
+  }
+
+  /// Get household by ID
+  static Future<Household?> getHousehold(String id) async {
+    final box = await getHouseholdsBox();
+    return box.values.firstWhere(
+      (h) => h.id == id,
+      orElse: () => throw Exception('Household not found'),
+    );
+  }
+
+  /// Save household
+  static Future<void> saveHousehold(Household household) async {
+    final box = await getHouseholdsBox();
+    await box.put(household.id, household);
+  }
+
   /// Clear all data
   static Future<void> clearAll() async {
     final box = await getFoodBox();