fix: harden school imports and add optional feedback diagnostics

mobile/lib/app/app_controller.dart

@@ -6,6 +6,7 @@ import '../domain/app_settings.dart';
 import '../data/snapshot_store.dart';
 import '../data/json_schedule_import.dart';
 import '../services/notification_service.dart';
+import '../services/diagnostic_log.dart';
 import '../services/calendar_service.dart';
 import '../domain/schedule_engine.dart';
 import '../data/demo_schedule.dart';
@@ -40,6 +41,10 @@ class AppController extends ChangeNotifier {
         await operation();
       } catch (error) {
         lastError = error.toString();
+        DiagnosticLog.instance.add(
+          'operation_failed',
+          fields: {'code': error.runtimeType.toString()},
+        );
       }
       notifyListeners();
     });
@@ -57,6 +62,10 @@ class AppController extends ChangeNotifier {
     await store.save(next);
     snapshot = next;
     lastError = null;
+    DiagnosticLog.instance.add(
+      'snapshot_saved',
+      fields: {'count': next.courses.length, 'term': next.schoolTerm?.id},
+    );
   }
 
   Future<void> initialize({bool reconcileServices = true}) => _run(() async {
@@ -171,6 +180,8 @@ class AppController extends ChangeNotifier {
         schoolTerm: draft.schoolTerm,
         clearExams:
             draft.schoolTerm?.school != SupportedSchool.uestcUndergraduate &&
+            snapshot.examSchedule?.school !=
+                SupportedSchool.uestcUndergraduate &&
             _differentTerm(draft.schoolTerm),
         settings: _differentTerm(draft.schoolTerm)
             ? snapshot.settings.copyWith(clearSemester: true)
@@ -359,12 +370,23 @@ class AppController extends ChangeNotifier {
         clock(),
       );
       reminderErrorCode = null;
+      DiagnosticLog.instance.add(
+        'reminders_reconciled',
+        fields: {
+          'count': occurrences.length,
+          'status': reminderResult.status.name,
+        },
+      );
     } catch (error) {
       reminderErrorCode = error is ReminderSetupException
           ? error.code
           : error is PlatformException
           ? error.code
           : error.runtimeType.toString();
+      DiagnosticLog.instance.add(
+        'reminders_failed',
+        fields: {'code': error.runtimeType.toString()},
+      );
       reminderResult = ReminderResult(
         ReminderStatus.error,
         message: error is ReminderSetupException