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/inventory/screens/add_item_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:intl/intl.dart';
 import '../../../core/constants/colors.dart';
+import '../../../data/local/hive_database.dart';
 import '../models/food_item.dart';
 import '../controllers/inventory_controller.dart';
 import '../services/barcode_service.dart';
@@ -118,6 +119,9 @@ class _AddItemScreenState extends ConsumerState<AddItemScreen> {
 
   Future<void> _saveItem() async {
     if (_formKey.currentState!.validate()) {
+      // Get current household ID from settings
+      final settings = await HiveDatabase.getSettings();
+
       final item = FoodItem()
         ..name = _nameController.text.trim()
         ..barcode = _barcode
@@ -132,6 +136,7 @@ class _AddItemScreenState extends ConsumerState<AddItemScreen> {
         ..notes = _notesController.text.trim().isEmpty
             ? null
             : _notesController.text.trim()
+        ..householdId = settings.currentHouseholdId
         ..lastModified = DateTime.now();
 
       try {