feat(portal-shell): grades 模块 5 页迁移（教师域 §9.1 B2）

§9.1 B2 grades 行：/grades、/entry、/analytics、/stats、/report-card
契约：grade(id) ✅ 真实查询；列表/分析/统计/成绩单 → MSW 兜底

新增文件：
- src/lib/api/grades.ts (6 hooks)
- src/lib/api/operations/grades.graphql.ts (6 documents)
- src/features/teacher/grades/ (7 files: transformations + tests + 5 clients)
- src/app/shell/teacher/grades/ (5 page.tsx + loading.tsx + error.tsx)

修改文件：
- src/mocks/graphql-data.ts (5 mock 常量 + 6 handler cases)
- src/messages/{zh-CN,en}.json (grades i18n)
- src/lib/api/{index,operations/index}.ts (导出 grades)
- scripts/check-page-count.ts (baseline 26 → 31)

DoD 验收（§11.3 11 项）：
- typecheck 0 errors
- lint 0 errors
- vitest 357 tests passed
- lint:tokens 0 errors
- check:pages 31 PASS

关联：ARCHITECTURE.md §5.3 / §5.4 / §9.1 / §10 P2 / §11.3 / §11.4

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

@@ -19,9 +19,9 @@ interface Baseline {
   categories: Record<string, { pattern: string; min: number; label: string }>;
 }
 
-// Baseline as of P2 (2026-07-22, homework module added). Update when adding pages.
+// Baseline as of P2 (2026-07-22, grades module added). Update when adding pages.
 const BASELINE: Baseline = {
-  total: 26,
+  total: 31,
   categories: {
     dashboards: {
       pattern: "shell/{admin,teacher,student,parent}/page.tsx",