fix(attendance): 默认周范围改为中国日期周一起点

generateFromSchedules / getCalendar 原来用本地周一零点转 UTC 日期，
在上海时区会得到前一天的日期，导致默认范围变成周日~周日（8 天）。
改为 dayjs().utcOffset(8) 按中国日期计算，与 getTodayDateOnly 语义一致。

新增测试锁定：默认周 = 本周一~本周日，周日晚上仍归本周，显式传参原样透传。

apps/server/src/attendance/attendance-calendar.service.spec.ts

@@ -0,0 +1,44 @@
+import { AttendanceCalendarService } from './attendance-calendar.service';
+
+describe('AttendanceCalendarService — 默认周起点', () => {
+  function createService() {
+    return new AttendanceCalendarService({} as never, {} as never);
+  }
+
+  afterEach(() => jest.useRealTimers());
+
+  it('未传 weekStart 时默认本周一（中国日期）', async () => {
+    jest.useFakeTimers().setSystemTime(new Date('2026-08-05T10:00:00+08:00')); // 周三
+    const service = createService();
+    const spy = jest
+      .spyOn(service as never, 'buildCalendar' as never)
+      .mockResolvedValue([] as never);
+
+    await service.getCalendar({ classId: 1 } as never);
+
+    expect(spy).toHaveBeenCalledWith(1, '2026-08-03');
+  });
+
+  it('周日晚间仍归入本周一', async () => {
+    jest.useFakeTimers().setSystemTime(new Date('2026-08-09T22:00:00+08:00')); // 周日晚上
+    const service = createService();
+    const spy = jest
+      .spyOn(service as never, 'buildCalendar' as never)
+      .mockResolvedValue([] as never);
+
+    await service.getCalendar({ classId: 1 } as never);
+
+    expect(spy).toHaveBeenCalledWith(1, '2026-08-03');
+  });
+
+  it('传入 weekStart 时原样透传', async () => {
+    const service = createService();
+    const spy = jest
+      .spyOn(service as never, 'buildCalendar' as never)
+      .mockResolvedValue([] as never);
+
+    await service.getCalendar({ classId: 1, weekStart: '2026-08-10' } as never);
+
+    expect(spy).toHaveBeenCalledWith(1, '2026-08-10');
+  });
+});