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/grades/components/grade-stats-card.tsx

@@ -1,27 +1,8 @@
 import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
+import { StatItem } from "@/shared/components/ui/stat-item"
 import { TrendingUp, TrendingDown, BarChart3, Target, Award, CheckCircle2 } from "lucide-react"
 import type { GradeStats } from "../types"
 
-interface StatItemProps {
-  label: string
-  value: string | number
-  icon: React.ReactNode
-  hint?: string
-}
-
-function StatItem({ label, value, icon, hint }: StatItemProps) {
-  return (
-    <div className="flex flex-col gap-1 rounded-lg border bg-card p-4">
-      <div className="flex items-center justify-between">
-        <span className="text-xs font-medium text-muted-foreground">{label}</span>
-        <span className="text-muted-foreground">{icon}</span>
-      </div>
-      <span className="text-2xl font-bold">{value}</span>
-      {hint ? <span className="text-xs text-muted-foreground">{hint}</span> : null}
-    </div>
-  )
-}
-
 export function GradeStatsCard({ stats }: { stats: GradeStats | null }) {
   if (!stats || stats.count === 0) {
     return (