feat: add local reminders and owned calendar synchronization

mobile/test/app/app_controller_test.dart

@@ -35,6 +35,63 @@ void main() {
     );
   });
   tearDown(() => controller.dispose());
+  test(
+    'failed calendar cleanup is retried after reopening while sync is off',
+    () async {
+      final provider = CleanupCalendar()..failDelete = true;
+      final first = AppController(
+        store,
+        notifications,
+        provider,
+        controller.clock,
+      );
+      await first.initialize();
+      await first.disableCalendar(deleteEvents: true);
+      expect(first.lastError, isNotNull);
+      first.dispose();
+      provider.failDelete = false;
+      final reopened = AppController(
+        store,
+        notifications,
+        provider,
+        controller.clock,
+      );
+      await reopened.initialize();
+      expect(provider.deletions, 2);
+      expect(reopened.snapshot.settings.calendarEnabled, isFalse);
+      reopened.dispose();
+    },
+  );
+  test(
+    'notification cleanup failure does not prevent calendar cleanup',
+    () async {
+      final broken = AppController(
+        store,
+        BrokenCancellation(),
+        calendar,
+        controller.clock,
+      );
+      await broken.initialize();
+      await broken.clearCourses();
+      expect(calendar.deletions, 1);
+      expect(broken.snapshot.courses, isEmpty);
+      broken.dispose();
+    },
+  );
+  test(
+    'denied calendar permission and unavailable calendars stay off',
+    () async {
+      await controller.initialize();
+      calendar.access = false;
+      await controller.enableCalendarFromUserAction('local');
+      expect(controller.snapshot.settings.calendarEnabled, isFalse);
+      expect(controller.calendarSyncError, isNotNull);
+      calendar.access = true;
+      await controller.enableCalendarFromUserAction('readonly-or-missing');
+      expect(controller.snapshot.settings.calendarEnabled, isFalse);
+      expect(calendar.synchronizations, 0);
+    },
+  );
   test('a new successful demo action clears a stale save error', () async {
     await controller.initialize();
     store.failSave = true;
@@ -121,3 +178,19 @@ class DamagedStore extends MemoryStore {
   @override
   Future<AppSnapshot?> load() async => throw const FormatException('damaged');
 }
+
+class CleanupCalendar extends FakeCalendar {
+  bool failDelete = false;
+  @override
+  Future<void> deleteOwned(Map<String, String> ids) async {
+    deletions++;
+    if (failDelete) {
+      throw StateError('denied');
+    }
+  }
+}
+
+class BrokenCancellation extends FakeNotifications {
+  @override
+  Future<void> cancelOwned() async => throw StateError('denied');
+}