feat(portal-shell): questions + textbooks 模块 3 页迁移（教师域 §9.1 B2）

§9.1 line 630-631 教师域：
- /shell/teacher/questions (列表，1 页)
- /shell/teacher/textbooks + /shell/teacher/textbooks/[id] (列表+详情，2 页)
契约：🟡 混合
- question(id) ✅ 真实单查（schema 第 775-778 行确认）
- textbook(id) ✅ 真实单查
- 列表查询 ❌ schema 无 → MSW 兜底 + @contract-pending
- textbookChapters(textbookId) ❌ schema 无 → MSW 兜底

新增文件：
- src/lib/api/questions.ts (5 hooks)
- src/lib/api/textbooks.ts (5 hooks)
- src/lib/api/operations/{questions,textbooks}.graphql.ts (10 documents)
- src/features/teacher/questions/ (clients + transformations + tests)
- src/features/teacher/textbooks/ (clients + transformations + tests)
- src/app/shell/teacher/{questions,textbooks}/ (3 page.tsx + 2 loading + 2 error)

修改文件：
- src/lib/api/teacher.ts + operations/teacher.graphql.ts
  → 重命名 legacy widget API 以解决命名冲突：
    Question → QuestionBankItem
    Textbook → LegacyTextbook
    Chapter → LegacyChapter
    TextbookFilter → LegacyTextbookFilter
    useTextbooks → useLegacyTextbooks
    GET_QUESTIONS_DOC → GET_QUESTION_BANK_DOC
    GET_TEXTBOOKS_DOC → GET_LEGACY_TEXTBOOKS_DOC
- src/widgets/teacher/{question-bank,textbook-manager}/index.tsx
  → 更新引用为重命名后的 legacy API
- src/mocks/graphql-data.ts
  → 添加 questions/textbooks mock + GetQuestionBank/GetLegacyTextbooks handler
- src/messages/{zh-CN,en}.json (questions + textbooks i18n)
- src/lib/api/{index,operations/index}.ts (导出 questions + textbooks)
- src/shared/lib/route-permissions.ts (questions + textbooks 路由权限)
- scripts/check-page-count.ts (baseline 37 → 40)

DoD 验收（§11.3 11 项）：
- typecheck 0 errors
- lint 0 errors
- vitest 469 tests passed (新增 64 tests)
- lint:tokens 0 errors
- check:pages 40 PASS
- route-permissions 已声明
- 三态齐备
- @contract-pending + MSW 兜底
- i18n zh-CN + en 同步

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/src/lib/api/operations/index.ts

@@ -8,6 +8,8 @@ export * from "./exams.graphql";
 export * from "./homework.graphql";
 export * from "./grades.graphql";
 export * from "./lesson-plans.graphql";
+export * from "./questions.graphql";
+export * from "./textbooks.graphql";
 export * from "./student.graphql";
 export * from "./parent.graphql";
 export * from "./admin.graphql";