feat(01-02): wire app.dart and main.dart for launchable app

- App widget with MaterialApp.router, theme/darkTheme from AppTheme, themeMode from ThemeNotifier
- German localization delegates configured, debug banner disabled
- main.dart wraps App in ProviderScope with ensureInitialized
- All 16 tests pass, dart analyze clean, flutter build apk succeeds

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/main.dart

@@ -1,6 +1,9 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import 'package:household_keeper/app.dart';
+
 void main() {
-  runApp(const ProviderScope(child: MaterialApp(home: Scaffold())));
+  WidgetsFlutterBinding.ensureInitialized();
+  runApp(const ProviderScope(child: App()));
 }