feat(portal-shell): attendance + classes + students 模块 8 页迁移（教师域 §9.1 B2）

§9.1 line 632-634 教师域：
- /shell/teacher/attendance (列表) / /sheet (表单) / /report (报表) / /stats (统计) — 4 页
- /shell/teacher/classes (列表) / /[id] (详情) / /schedule (课表) — 3 页
- /shell/teacher/students (列表) — 1 页
契约：
- attendance 全 ❌ → MSW 兜底
- classes 🟡 classInfo(id) ✅ 真实单查 + 列表 ❌ MSW
- students 全 ❌ → MSW 兜底

新增文件：
- src/lib/api/{attendance,classes,students}.ts (14 hooks 合计)
- src/lib/api/operations/{attendance,classes,students}.graphql.ts (14 documents)
- src/features/teacher/{attendance,classes,students}/ (clients + transformations + tests)
- src/app/shell/teacher/{attendance,classes,students}/ (8 page.tsx + 3 loading + 3 error)

修改文件：
- src/mocks/graphql-data.ts (12 mock 数据 + handler cases)
- src/messages/{zh-CN,en}.json (attendance/classes/students i18n 命名空间)
- src/lib/api/{index,operations/index}.ts (导出 attendance/classes/students)
- src/shared/lib/route-permissions.ts (attendance/classes/students 路由权限)
- scripts/check-page-count.ts (baseline 40 → 48)

DoD 验收（§11.3 11 项）：
- typecheck 0 errors
- lint 0 errors
- vitest 566 tests passed
- lint:tokens 0 errors
- check:pages 48 PASS
- route-permissions 已声明
- 三态齐备
- @contract-pending + MSW 兜底
- i18n zh-CN + en 同步

设计决策：
- classes/[id] 走真实 classInfo(id) 查询
- 无 STUDENT_* 权限点，students 路由复用 CLASS_READ/CLASS_MANAGE

关联：ARCHITECTURE.md §5.3 / §5.4 / §5.5 / §9.1 / §10 P2 / §11.3 / §11.4
契约工单：docs/architecture/issues/contracts/core-edu_contract.md

apps/portal-shell/scripts/check-page-count.ts

@@ -19,9 +19,10 @@ interface Baseline {
   categories: Record<string, { pattern: string; min: number; label: string }>;
 }
 
-// Baseline as of P2 (2026-07-22, questions + textbooks modules added). Update when adding pages.
+// Baseline as of P2 B2 (2026-07-22, attendance + classes + students modules added).
+// Update when adding pages.
 const BASELINE: Baseline = {
-  total: 40,
+  total: 48,
   categories: {
     dashboards: {
       pattern: "shell/{admin,teacher,student,parent}/page.tsx",