feat: integrate undergraduate school workflows and period twelve

mobile/test/domain/schedule_engine_test.dart

@@ -106,7 +106,7 @@ void main() {
   });
   test('invalid lesson, weekday and week values are rejected', () {
     expect(() => course(first: 0), throwsArgumentError);
-    expect(() => course(last: 12), throwsArgumentError);
+    expect(() => course(last: 13), throwsArgumentError);
     expect(() => course(day: 8), throwsArgumentError);
     expect(() => course(weeks: {0}), throwsArgumentError);
     expect(

mobile/test/domain/undergraduate_models_test.dart

@@ -7,6 +7,37 @@ import 'package:hepan_everyday/domain/app_snapshot.dart';
 import 'package:hepan_everyday/domain/course.dart';
 
 void main() {
+  test(
+    'managed undergraduate identifiers cannot lose their school or term',
+    () {
+      final c = Course(
+        id: 'uestc-undergraduate-523-managed',
+        name: '课程',
+        teacher: '教师',
+        room: '教室',
+        weekday: 1,
+        startPeriod: 1,
+        endPeriod: 2,
+        weeks: {1},
+        source: CourseSource.school,
+      );
+      final saved = AppSnapshot(
+        courses: [c],
+        schoolTerm: SchoolTerm(523, school: SupportedSchool.uestcUndergraduate),
+      ).toJson();
+      expect(
+        () => AppSnapshot.fromJson({
+          ...saved,
+          'schoolTerm': {'id': 73},
+        }),
+        throwsFormatException,
+      );
+      expect(
+        () => AppSnapshot.fromJson({...saved, 'schoolTerm': null}),
+        throwsFormatException,
+      );
+    },
+  );
   SchoolTerm under(int id) =>
       SchoolTerm(id, school: SupportedSchool.uestcUndergraduate);
   test('undergraduate semester labels and final exam URLs', () {