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/assignments/[assignmentId]/loading.tsx

@@ -0,0 +1,13 @@
+import { Skeleton } from "@/shared/components/ui/skeleton"
+
+export default function Loading() {
+  return (
+    <div className="space-y-4">
+      <div className="space-y-2">
+        <Skeleton className="h-8 w-64" />
+        <Skeleton className="h-4 w-48" />
+      </div>
+      <Skeleton className="h-96 w-full" />
+    </div>
+  )
+}

src/app/(dashboard)/student/learning/assignments/[assignmentId]/page.tsx

@@ -24,7 +24,7 @@ export default async function StudentAssignmentTakePage({
   const status = data.submission?.status
   if (status === "graded" || status === "submitted") {
     return (
-      <div className="flex h-full flex-col space-y-4 p-6">
+      <div className="h-full flex-1 flex-col space-y-8 p-8 md:flex">
         <div className="flex flex-col gap-1">
           <h2 className="text-2xl font-bold tracking-tight">{data.assignment.title}</h2>
           <div className="text-sm text-muted-foreground">
@@ -43,7 +43,7 @@ export default async function StudentAssignmentTakePage({
         <h2 className="text-2xl font-bold tracking-tight">{data.assignment.title}</h2>
         <div className="text-sm text-muted-foreground">
           <span>Due: {data.assignment.dueAt ? formatDate(data.assignment.dueAt) : "-"}</span>
-          <span className="mx-2">•</span>
+          <span className="mx-2" aria-hidden="true">•</span>
           <span>Max Attempts: {data.assignment.maxAttempts}</span>
         </div>
       </div>