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/homework/assignments/[id]/page.tsx

@@ -7,7 +7,7 @@ import { HomeworkAssignmentQuestionErrorOverviewCard } from "@/modules/homework/
 import { Badge } from "@/shared/components/ui/badge"
 import { Button } from "@/shared/components/ui/button"
 import { formatDate } from "@/shared/lib/utils"
-import { ChevronLeft, Users, Calendar, BarChart3, CheckCircle2 } from "lucide-react"
+import { ArrowLeft, Users, Calendar, BarChart3, CheckCircle2 } from "lucide-react"
 
 export const dynamic = "force-dynamic"
 
@@ -25,14 +25,12 @@ export default async function HomeworkAssignmentDetailPage({ params }: { params:
       <div className="border-b bg-background px-8 py-5">
         <div className="flex flex-col gap-4 md:flex-row md:items-start md:justify-between">
           <div className="min-w-0 flex flex-col gap-2">
-            <div className="flex items-center gap-2 text-sm text-muted-foreground mb-1">
-              <Link href="/teacher/homework/assignments" className="flex items-center hover:text-foreground transition-colors">
-                <ChevronLeft className="h-4 w-4 mr-1" aria-hidden="true" />
-                Assignments
+            <Button asChild variant="ghost" size="sm" className="w-fit">
+              <Link href="/teacher/homework/assignments">
+                <ArrowLeft className="mr-2 h-4 w-4" aria-hidden="true" />
+                返回作业列表
               </Link>
-              <span aria-hidden="true">/</span>
-              <span>Details</span>
-            </div>
+            </Button>
             <div className="flex items-center gap-3">
               <h1 className="text-2xl font-bold tracking-tight text-foreground line-clamp-2">{assignment.title}</h1>
               <Badge variant={assignment.status === "published" ? "default" : "secondary"} className="capitalize">