feat: compose Android app and verify native calendar and reminders

mobile/test/widgets/settings_test.dart

@@ -2,11 +2,44 @@ import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:timezone/data/latest.dart' as tzdata;
 import 'package:hepan_everyday/app/hepan_app.dart';
+import 'package:hepan_everyday/app/app_controller.dart';
+import 'package:hepan_everyday/features/profile/settings_page.dart';
+import 'package:hepan_everyday/services/calendar_service.dart';
+
+import '../support/fakes.dart';
 
 import 'navigation_test.dart' show uiController;
 
 void main() {
   setUpAll(tzdata.initializeTimeZones);
+  testWidgets('calendar provider failure is explained and keeps switch off', (
+    tester,
+  ) async {
+    final controller = AppController(
+      MemoryStore(),
+      FakeNotifications(),
+      UnavailableCalendar(),
+      DateTime.now,
+    );
+    await controller.initialize();
+    await tester.pumpWidget(
+      MaterialApp(home: SettingsPage(controller: controller)),
+    );
+    await tester.pumpAndSettle();
+    await tester.scrollUntilVisible(
+      find.text('导入手机日历'),
+      250,
+      scrollable: find.byType(Scrollable).first,
+    );
+    await tester.ensureVisible(find.text('导入手机日历'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('导入手机日历'));
+    await tester.pumpAndSettle();
+    expect(tester.takeException(), isNull);
+    expect(find.text('日历暂时不可用，请检查权限后重试'), findsOneWidget);
+    expect(controller.snapshot.settings.calendarEnabled, isFalse);
+    controller.dispose();
+  });
   testWidgets(
     'invalid semester weeks are rejected without changing saved data',
     (tester) async {
@@ -57,3 +90,9 @@ void main() {
     controller.dispose();
   });
 }
+
+class UnavailableCalendar extends FakeCalendar {
+  @override
+  Future<List<DeviceCalendar>> listWritableCalendars() async =>
+      throw StateError('unavailable');
+}