feat: 新增备课模块并修复全模块 P0/P1/P2 缺陷

主要变更:

- 新增 lesson-preparation 模块: 备课编辑器、节点编辑、AI 建议、知识点选择、版本历史、作业发布

- 新增 shared 通用组件: charts/question-bank-filters/schedule-list/ui (chip-nav/filter-bar/page-header/stat-card/stat-item)

- 新增 student/admin 端 loading.tsx 与 error.tsx, 优化加载与错误态体验

- 新增 teacher/lesson-plans 页面 (列表/新建/编辑)

- 新增 drizzle 迁移 0002_tiny_lionheart 及 snapshot

- 新增 textbooks/schema.ts 与 exams/utils/normalize-structure.ts

- 修复 Tiptap v3 SSR hydration 崩溃 (rich-text-block immediatelyRender: false)

- 重构多模块 data-access/actions/组件, 修复权限校验与类型规范

- 同步架构文档 004/005 反映新增模块、导出、依赖关系

- 归档 bugs/* 测试报告与 e2e 测试脚本 (admin/parent/student/teacher web_test)

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

@@ -1,4 +1,4 @@
-import { BookOpen, Inbox } from "lucide-react"
+import { BookOpen, UserX } from "lucide-react"
 
 import { getTextbooks } from "@/modules/textbooks/data-access"
 import { TextbookCard } from "@/modules/textbooks/components/textbook-card"
@@ -25,7 +25,7 @@ export default async function StudentTextbooksPage({
   if (!student) {
     return (
       <div className="h-full flex-1 flex-col space-y-8 p-8 md:flex">
-        <EmptyState title="No user found" description="Create a student user to see textbooks." icon={Inbox} />
+        <EmptyState title="No user found" description="Create a student user to see textbooks." icon={UserX} />
       </div>
     )
   }
@@ -39,15 +39,10 @@ export default async function StudentTextbooksPage({
 
   return (
     <div className="h-full flex-1 flex-col space-y-8 p-8 md:flex">
-      {/* <div className="flex flex-col gap-4 md:flex-row md:items-center md:justify-between">
-        <div>
-          <h2 className="text-2xl font-bold tracking-tight">Textbooks</h2>
-          <p className="text-muted-foreground">Browse your course textbooks.</p>
-        </div>
-        <Button asChild variant="outline">
-          <Link href="/student/dashboard">Back</Link>
-        </Button>
-      </div> */}
+      <div>
+        <h2 className="text-2xl font-bold tracking-tight">Textbooks</h2>
+        <p className="text-muted-foreground">Browse your course textbooks.</p>
+      </div>
 
       <TextbookFilters />