feat: add local reminders and owned calendar synchronization

mobile/lib/app/app_controller.dart

@@ -140,21 +140,33 @@ class AppController extends ChangeNotifier {
   });
   Future<void> clearCourses() => _run(() async {
     // Preserve ownership mapping until cleanup has actually succeeded.
-    await _save(snapshot.copyWith(courses: [], clearMetadata: true));
+    await _save(
+      snapshot.copyWith(
+        courses: [],
+        clearMetadata: true,
+        calendarCleanupPending: true,
+      ),
+    );
     isDemo = false;
-    await notifications.cancelOwned();
-    await calendar.deleteOwned(snapshot.calendarEventIds);
-    await _save(snapshot.copyWith(calendarEventIds: {}));
+    try {
+      await notifications.cancelOwned();
+    } catch (_) {
+      reminderResult = const ReminderResult(
+        ReminderStatus.error,
+        message: '提醒清理失败，可重试',
+      );
+    }
+    await _cleanupCalendar();
   });
   Future<void> disableCalendar({required bool deleteEvents}) => _run(() async {
     await _save(
       snapshot.copyWith(
         settings: snapshot.settings.copyWith(calendarEnabled: false),
+        calendarCleanupPending: deleteEvents || snapshot.calendarCleanupPending,
       ),
     );
     if (deleteEvents) {
-      await calendar.deleteOwned(snapshot.calendarEventIds);
-      await _save(snapshot.copyWith(calendarEventIds: {}));
+      await _cleanupCalendar();
     }
     calendarSyncError = null;
   });
@@ -166,6 +178,9 @@ class AppController extends ChangeNotifier {
           calendarSyncError = '日历权限未获允许';
           return;
         }
+        if (snapshot.calendarCleanupPending) {
+          await _cleanupCalendar();
+        }
         final calendars = await calendar.listWritableCalendars();
         if (!calendars.any((c) => c.id == calendarId)) {
           calendarSyncError = '请选择可写入的日历';
@@ -200,6 +215,26 @@ class AppController extends ChangeNotifier {
     await _reconcile();
   });
   Future<void> refreshServices() => _run(_reconcile);
+  Future<void> retryCalendarCleanup() => _run(() async {
+    if (await calendar.requestAccess()) {
+      await _cleanupCalendar();
+    } else {
+      calendarSyncError = '日历权限未获允许，课程日程尚未清理';
+    }
+  });
+  Future<void> _cleanupCalendar() async {
+    try {
+      await calendar.deleteOwned(snapshot.calendarEventIds);
+      await _save(
+        snapshot.copyWith(calendarEventIds: {}, calendarCleanupPending: false),
+      );
+      calendarSyncError = null;
+    } catch (_) {
+      calendarSyncError = '课程日程尚未清理，请允许日历访问后重试';
+      rethrow;
+    }
+  }
+
   Future<void> _reconcile() async {
     if (!storageReady) {
       return;
@@ -220,6 +255,13 @@ class AppController extends ChangeNotifier {
         message: '提醒设置未完成，可重试',
       );
     }
+    if (snapshot.calendarCleanupPending) {
+      try {
+        await _cleanupCalendar();
+      } catch (_) {
+        return;
+      }
+    }
     if (settings.calendarEnabled && settings.calendarId != null) {
       try {
         final ids = await calendar.sync(