fix(teacher): 统一详情页返回路径与中英文文案 (P1-3+P2-1)

P1-3: empty-state 默认按钮 variant 改为 outline 并新增 variant prop；button.tsx 导出 ButtonProps；统一 5 个详情页返回路径为 ghost+ArrowLeft+文字标签；course-plan-detail raw a 改为 Link。P2-1: formatLongDate 默认 locale 改为 zh-CN，weekday 改为 short；返回按钮文案中文化；course-plan-detail 全量中文化；grades/analytics 标题中文化。验证：tsc 0 错误，lint 0 错误，架构图 004/005 已同步。

src/app/(dashboard)/teacher/grades/analytics/page.tsx

@@ -46,14 +46,14 @@ export default async function GradeAnalyticsPage({
     return (
       <div className="h-full flex-1 flex-col space-y-8 p-8 md:flex">
         <div>
-          <h1 className="text-2xl font-bold tracking-tight">Grade Analytics</h1>
+          <h1 className="text-2xl font-bold tracking-tight">成绩分析</h1>
           <p className="text-muted-foreground">
-            Trend analysis, class comparisons, and score distributions.
+            趋势分析、班级对比与分数分布。
           </p>
         </div>
         <EmptyState
-          title="No classes"
-          description="You don't have any classes yet."
+          title="暂无班级"
+          description="您还没有任何班级。"
           icon={BarChart3}
           className="border-none shadow-none"
         />
@@ -98,15 +98,15 @@ export default async function GradeAnalyticsPage({
     <div className="h-full flex-1 flex-col space-y-6 p-8 md:flex">
       <div className="flex flex-col justify-between gap-4 md:flex-row md:items-center">
         <div>
-          <h1 className="text-2xl font-bold tracking-tight">Grade Analytics</h1>
+          <h1 className="text-2xl font-bold tracking-tight">成绩分析</h1>
           <p className="text-muted-foreground">
-            Trend analysis, class comparisons, and score distributions.
+            趋势分析、班级对比与分数分布。
           </p>
         </div>
-        <Button asChild variant="outline">
+        <Button asChild variant="ghost" size="sm">
           <Link href="/teacher/grades">
             <ArrowLeft className="mr-2 h-4 w-4" aria-hidden="true" />
-            Back to Grades
+            返回成绩列表
           </Link>
         </Button>
       </div>