feat(announcements,messaging): 公告与消息模块审计重构 — i18n + Error Boundary + a11y

- 新增审计报告 docs/architecture/audit/announcements-messages-audit-report.md
- 新增中英双语 i18n 字典 announcements.json / messages.json（11/13 个命名空间）
- 重构所有 announcements 和 messaging 组件接入 next-intl（useTranslations）
- 所有页面 page.tsx 使用 generateMetadata + getTranslations 替代硬编码 metadata
- 新增 7 个 error.tsx 错误边界（4 公告 + 3 消息），统一 EmptyState + i18n + 重试
- a11y 改进：announcement-card / message-list / notification-dropdown 添加 aria-label
- 同步架构图 004 和 005：i18n.messages 清单 + 已知问题修复记录

src/modules/announcements/components/announcement-card.tsx

@@ -1,32 +1,13 @@
 "use client"
 
 import Link from "next/link"
+import { useTranslations } from "next-intl"
+
 import { Badge } from "@/shared/components/ui/badge"
 import { Card, CardContent, CardHeader, CardTitle } from "@/shared/components/ui/card"
 import { formatDate } from "@/shared/lib/utils"
 import type { Announcement } from "../types"
 
-const STATUS_LABEL: Record<Announcement["status"], string> = {
-  draft: "Draft",
-  published: "Published",
-  archived: "Archived",
-}
-
-const STATUS_VARIANT: Record<
-  Announcement["status"],
-  "default" | "secondary" | "outline"
-> = {
-  draft: "secondary",
-  published: "default",
-  archived: "outline",
-}
-
-const TYPE_LABEL: Record<Announcement["type"], string> = {
-  school: "School",
-  grade: "Grade",
-  class: "Class",
-}
-
 export function AnnouncementCard({
   announcement,
   href,
@@ -34,12 +15,20 @@ export function AnnouncementCard({
   announcement: Announcement
   href?: string
 }) {
+  const t = useTranslations("announcements")
+
+  const statusVariant: Record<Announcement["status"], "default" | "secondary" | "outline"> = {
+    draft: "secondary",
+    published: "default",
+    archived: "outline",
+  }
+
   const card = (
     <Card className="h-full transition-colors hover:bg-accent/50">
       <CardHeader className="flex flex-row items-start justify-between gap-2 space-y-0">
         <CardTitle className="line-clamp-2 text-base">{announcement.title}</CardTitle>
-        <Badge variant={STATUS_VARIANT[announcement.status]} className="shrink-0">
-          {STATUS_LABEL[announcement.status]}
+        <Badge variant={statusVariant[announcement.status]} className="shrink-0">
+          {t(`status.${announcement.status}`)}
         </Badge>
       </CardHeader>
       <CardContent className="space-y-2">
@@ -48,15 +37,15 @@ export function AnnouncementCard({
         </p>
         <div className="flex flex-wrap items-center gap-2 text-xs text-muted-foreground">
           <Badge variant="outline" className="capitalize">
-            {TYPE_LABEL[announcement.type]}
+            {t(`type.${announcement.type}`)}
           </Badge>
           <span>
             {announcement.publishedAt
-              ? `Published ${formatDate(announcement.publishedAt)}`
-              : `Updated ${formatDate(announcement.updatedAt)}`}
+              ? t("meta.publishedAt", { date: formatDate(announcement.publishedAt) })
+              : t("meta.updatedAt", { date: formatDate(announcement.updatedAt) })}
           </span>
           {announcement.authorName ? (
-            <span className="ml-auto">by {announcement.authorName}</span>
+            <span className="ml-auto">{t("meta.author", { name: announcement.authorName })}</span>
           ) : null}
         </div>
       </CardContent>
@@ -65,7 +54,7 @@ export function AnnouncementCard({
 
   if (href) {
     return (
-      <Link href={href} className="block h-full">
+      <Link href={href} className="block h-full" aria-label={announcement.title}>
         {card}
       </Link>
     )