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/features/settings/models/app_settings.dart

@@ -19,11 +19,19 @@ class AppSettings extends HiveObject {
   @HiveField(4)
   String sortBy; // 'expiration', 'name', 'location'
 
+  @HiveField(5)
+  String? userName; // User's name for household sharing
+
+  @HiveField(6)
+  String? currentHouseholdId; // ID of the household they're in
+
   AppSettings({
     this.discordWebhookUrl,
     this.expirationAlertsEnabled = true,
     this.discordNotificationsEnabled = false,
     this.defaultView = 'grid',
     this.sortBy = 'expiration',
+    this.userName,
+    this.currentHouseholdId,
   });
 }