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/app.dart

@@ -0,0 +1,27 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import 'package:household_keeper/core/router/router.dart';
+import 'package:household_keeper/core/theme/app_theme.dart';
+import 'package:household_keeper/core/theme/theme_provider.dart';
+import 'package:household_keeper/l10n/app_localizations.dart';
+
+class App extends ConsumerWidget {
+  const App({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final themeMode = ref.watch(themeProvider);
+
+    return MaterialApp.router(
+      routerConfig: router,
+      theme: AppTheme.lightTheme(),
+      darkTheme: AppTheme.darkTheme(),
+      themeMode: themeMode,
+      localizationsDelegates: AppLocalizations.localizationsDelegates,
+      supportedLocales: const [Locale('de')],
+      locale: const Locale('de'),
+      debugShowCheckedModeBanner: false,
+    );
+  }
+}