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/courses/page.tsx

@@ -1,4 +1,4 @@
-import { Inbox } from "lucide-react"
+import { UserX } from "lucide-react"
 
 import { getStudentClasses } from "@/modules/classes/data-access"
 import { getCurrentStudentUser } from "@/modules/users/data-access"
@@ -11,7 +11,7 @@ export default async function StudentCoursesPage() {
   const student = await getCurrentStudentUser()
   if (!student) {
     return (
-      <div className="flex h-full flex-col space-y-8 p-8">
+      <div className="h-full flex-1 flex-col space-y-8 p-8 md:flex">
         <div>
           <h2 className="text-2xl font-bold tracking-tight">Courses</h2>
           <p className="text-muted-foreground">Your enrolled classes.</p>
@@ -19,7 +19,7 @@ export default async function StudentCoursesPage() {
         <EmptyState
           title="No user found"
           description="Create a student user to see courses."
-          icon={Inbox}
+          icon={UserX}
         />
       </div>
     )