feat: keep undergraduate exams independent of course terms

mobile/lib/app/app_controller.dart

@@ -11,6 +11,7 @@ import '../domain/schedule_engine.dart';
 import '../data/demo_schedule.dart';
 import '../domain/exam_schedule.dart';
 import '../domain/school_term.dart';
+import '../domain/school_identity.dart';
 
 class AppController extends ChangeNotifier {
   AppController(this.store, this.notifications, this.calendar, this.clock);
@@ -89,6 +90,15 @@ class AppController extends ChangeNotifier {
   Future<void> leaveDemo() => _run(() async {
     isDemo = false;
   });
+  Future<bool> selectSchool(SupportedSchool school) async {
+    var saved = false;
+    await _run(() async {
+      await _save(snapshot.copyWith(selectedSchool: school));
+      saved = true;
+    });
+    return saved;
+  }
+
   Future<void> updateSettings(
     AppSettings Function(AppSettings current) change,
   ) => _run(() async {
@@ -148,11 +158,17 @@ class AppController extends ChangeNotifier {
     if (draft.courses.any((c) => c.source != draft.source)) {
       throw const FormatException('课程来源不一致');
     }
+    if (draft.schoolTerm?.school != SupportedSchool.uestcUndergraduate &&
+        draft.courses.any((c) => c.endPeriod > 11)) {
+      throw const FormatException('第12节需要本科课表来源');
+    }
     await _save(
       snapshot.copyWith(
         courses: draft.courses,
         schoolTerm: draft.schoolTerm,
-        clearExams: _differentTerm(draft.schoolTerm),
+        clearExams:
+            draft.schoolTerm?.school != SupportedSchool.uestcUndergraduate &&
+            _differentTerm(draft.schoolTerm),
         settings: _differentTerm(draft.schoolTerm)
             ? snapshot.settings.copyWith(clearSemester: true)
             : snapshot.settings,
@@ -188,6 +204,10 @@ class AppController extends ChangeNotifier {
   });
   Future<void> applyExams(ExamSchedule value) => _run(() async {
     final validated = ExamSchedule.fromJson(value.toJson());
+    if (validated.school == SupportedSchool.uestcUndergraduate) {
+      await _save(snapshot.copyWith(examSchedule: validated));
+      return;
+    }
     final term = SchoolTerm(int.parse(validated.termId));
     final changed = _differentTerm(term);
     await _save(