feat(textbooks): 教材模块审计重构 — 跨模块解耦 + 权限 + i18n + 错误边界 + 纯函数抽取

P0 修复：
- 解耦跨模块 UI 依赖：knowledge-point-dialogs 不再直接 import questions，
  改为 renderQuestionCreator render prop 由页面注入
- 接入 usePermission Hook 替换 canEdit 硬编码
- 全模块 i18n 改造：新增 en/zh-CN 翻译文件，替换所有硬编码文案
- Server Action 资源归属校验：新增 verifyChapterBelongsToTextbook/
  verifyKnowledgePointBelongsToTextbook，在 reorder/update/delete/create 中校验

P1 改进：
- 补齐 Error Boundary：4 个 error.tsx + TextbookSectionErrorBoundary 区块包裹
- 抽取纯函数到 utils.ts/graph-layout.ts/constants.ts 并补单测（26 用例全通过）
- 消除重复组件：删除 knowledge-point-panel/create-knowledge-point-dialog
- 修复类型断言：chapter.children! → 守卫式访问
- 图谱 a11y：添加 role/aria-label/aria-pressed
- 统一删除确认：confirm() → AlertDialog
- 数据范围过滤：getTextbooksWithScope 支持学生端按年级过滤

P2 预留：
- TextbookAnalytics 埋点接口 + Provider + Hook

同步 005 架构数据 JSON：补充 getTextbooksWithScope/verify*/ChapterTreeNode 等

src/app/(dashboard)/student/learning/textbooks/[id]/page.tsx

@@ -1,4 +1,5 @@
 import { notFound } from "next/navigation"
+import { getTranslations } from "next-intl/server"
 
 import { BookOpen } from "lucide-react"
 
@@ -7,6 +8,7 @@ import { TextbookReader } from "@/modules/textbooks/components/textbook-reader"
 import { Badge } from "@/shared/components/ui/badge"
 import { EmptyState } from "@/shared/components/ui/empty-state"
 import { getCurrentStudentUser } from "@/modules/users/data-access"
+import { getGradeNameById } from "@/modules/school/data-access"
 
 export const dynamic = "force-dynamic"
 
@@ -15,6 +17,7 @@ export default async function StudentTextbookDetailPage({
 }: {
   params: Promise<{ id: string }>
 }) {
+  const t = await getTranslations("textbooks")
   const student = await getCurrentStudentUser()
   if (!student) return notFound()
 
@@ -28,6 +31,13 @@ export default async function StudentTextbookDetailPage({
 
   if (!textbook) notFound()
 
+  // P1-1 数据范围过滤：校验教材年级与学生年级匹配
+  // student.gradeId 是 grades 表 id，需解析为年级名称后才能与 textbooks.grade 字符串比较
+  const studentGradeName = student.gradeId ? await getGradeNameById(student.gradeId) : null
+  if (studentGradeName && textbook.grade && textbook.grade !== studentGradeName) {
+    notFound()
+  }
+
   return (
     <div className="flex h-[calc(100vh-4rem-3rem)] flex-col overflow-hidden bg-muted/5">
       <div className="flex items-center justify-between border-b bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/60 py-3 px-6 shrink-0 z-10">
@@ -48,13 +58,14 @@ export default async function StudentTextbookDetailPage({
           <div className="h-full flex items-center justify-center rounded-lg border border-dashed bg-card">
             <EmptyState
               icon={BookOpen}
-              title="No chapters"
-              description="This textbook has no chapters yet."
+              title={t("reader.noChapters")}
+              description={t("reader.noChaptersDesc")}
               className="border-none shadow-none"
             />
           </div>
         ) : (
           <div className="h-full min-h-0 max-w-[1600px] mx-auto w-full">
+            {/* 学生端不传 renderQuestionCreator，无题目创建权限 */}
             <TextbookReader chapters={chapters} knowledgePoints={knowledgePoints} />
           </div>
         )}