Add test helpers for widget testing

Provides reusable MaterialApp wrappers with localization
support for Flutter widget tests.

test/helpers/test_helpers.dart

@@ -0,0 +1,57 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_localizations/flutter_localizations.dart';
+import 'package:agenda_tasks/l10n/app_localizations.dart';
+
+/// Wraps a widget with MaterialApp and localization support for testing
+Widget createTestableWidget(Widget child) {
+  return MaterialApp(
+    localizationsDelegates: const [
+      AppLocalizations.delegate,
+      GlobalMaterialLocalizations.delegate,
+      GlobalWidgetsLocalizations.delegate,
+      GlobalCupertinoLocalizations.delegate,
+    ],
+    supportedLocales: const [
+      Locale('en'),
+      Locale('de'),
+    ],
+    locale: const Locale('en'),
+    home: Scaffold(body: child),
+  );
+}
+
+/// Wraps a widget with MaterialApp for testing (no Scaffold)
+Widget createTestableWidgetNoScaffold(Widget child) {
+  return MaterialApp(
+    localizationsDelegates: const [
+      AppLocalizations.delegate,
+      GlobalMaterialLocalizations.delegate,
+      GlobalWidgetsLocalizations.delegate,
+      GlobalCupertinoLocalizations.delegate,
+    ],
+    supportedLocales: const [
+      Locale('en'),
+      Locale('de'),
+    ],
+    locale: const Locale('en'),
+    home: child,
+  );
+}
+
+/// Wraps a page widget with MaterialApp and navigation for testing
+Widget createTestablePageWidget(Widget child) {
+  return MaterialApp(
+    localizationsDelegates: const [
+      AppLocalizations.delegate,
+      GlobalMaterialLocalizations.delegate,
+      GlobalWidgetsLocalizations.delegate,
+      GlobalCupertinoLocalizations.delegate,
+    ],
+    supportedLocales: const [
+      Locale('en'),
+      Locale('de'),
+    ],
+    locale: const Locale('en'),
+    home: child,
+  );
+}