feat: refactor API paths for authentication, inventory, and recipes; add contract tests for repositories

flutter/lib/features/inventory/presentation/create_inventory_screen.dart

@@ -3,6 +3,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
 import '../../../core/api/api_error_mapper.dart';
+import '../../../core/api/api_paths.dart';
 import '../../../core/api/api_providers.dart';
 import '../../../core/forms/form_options.dart';
 import '../../auth/data/auth_providers.dart';
@@ -54,7 +55,7 @@ class _CreateInventoryScreenState
     try {
       final token = await ref.read(authStateProvider.future);
       final api = ref.read(apiClientProvider);
-      final data = await api.getJson('/products', token: token);
+      final data = await api.getJson(ProductApiPaths.list, token: token);
       if (mounted) {
         setState(() {
           _products = (data as List<dynamic>)