Add feedback service, reminder diagnostics and smooth week transitions

mobile/lib/app/app_controller.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
 
 import '../domain/app_snapshot.dart';
 import '../domain/app_settings.dart';
@@ -24,6 +25,7 @@ class AppController extends ChangeNotifier {
   AppSettings? _demoSettings;
   Future<void> _queue = Future.value();
   String? lastError, calendarSyncError;
+  String? reminderErrorCode;
   ReminderResult reminderResult = const ReminderResult(ReminderStatus.off);
   List<Course> get visibleCourses => isDemo ? _demo : snapshot.courses;
   AppSettings get visibleSettings =>
@@ -331,10 +333,18 @@ class AppController extends ChangeNotifier {
         settings,
         clock(),
       );
-    } catch (_) {
-      reminderResult = const ReminderResult(
+      reminderErrorCode = null;
+    } catch (error) {
+      reminderErrorCode = error is ReminderSetupException
+          ? error.code
+          : error is PlatformException
+          ? error.code
+          : error.runtimeType.toString();
+      reminderResult = ReminderResult(
         ReminderStatus.error,
-        message: '提醒设置未完成，可重试',
+        message: error is ReminderSetupException
+            ? error.message
+            : '提醒设置未完成，请点击“检查提醒”后重试。',
       );
     }
     if (snapshot.calendarCleanupPending) {