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/modules/messaging/components/message-compose.tsx

@@ -1,6 +1,7 @@
 "use client"
 
 import { useState } from "react"
+import Link from "next/link"
 import { useRouter } from "next/navigation"
 import { toast } from "sonner"
 import { ArrowLeft, Send } from "lucide-react"
@@ -70,9 +71,9 @@ export function MessageCompose({
       <CardHeader>
         <div className="flex items-center gap-2">
           <Button asChild variant="ghost" size="icon">
-            <a href={backHref}>
+            <Link href={backHref}>
               <ArrowLeft className="h-4 w-4" />
-            </a>
+            </Link>
           </Button>
           <CardTitle>{parentMessageId ? "Reply" : "New Message"}</CardTitle>
         </div>