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/messaging/components/notification-dropdown.tsx

@@ -3,6 +3,7 @@
 import { useEffect, useState } from "react"
 import Link from "next/link"
 import { useRouter } from "next/navigation"
+import { useTranslations } from "next-intl"
 import { Bell, CheckCheck, MessageSquare, Megaphone, PenTool, GraduationCap } from "lucide-react"
 
 import { Badge } from "@/shared/components/ui/badge"
@@ -34,6 +35,7 @@ const TYPE_ICON: Record<NotificationType, typeof Bell> = {
 }
 
 export function NotificationDropdown() {
+  const t = useTranslations("messages")
   const router = useRouter()
   const [notifications, setNotifications] = useState<Notification[]>([])
   const [unreadCount, setUnreadCount] = useState(0)
@@ -96,8 +98,8 @@ export function NotificationDropdown() {
   return (
     <DropdownMenu open={open} onOpenChange={setOpen}>
       <DropdownMenuTrigger asChild>
-        <Button variant="ghost" size="icon" className="relative text-muted-foreground">
-          <Bell className="size-5" />
+        <Button variant="ghost" size="icon" className="relative text-muted-foreground" aria-label={t("title.notifications")}>
+          <Bell className="size-5" aria-hidden="true" />
           {unreadCount > 0 ? (
             <Badge
               variant="destructive"
@@ -106,20 +108,20 @@ export function NotificationDropdown() {
               {unreadCount > 9 ? "9+" : unreadCount}
             </Badge>
           ) : null}
-          <span className="sr-only">Notifications</span>
+          <span className="sr-only">{t("title.notifications")}</span>
         </Button>
       </DropdownMenuTrigger>
       <DropdownMenuContent align="end" className="w-80 p-0">
         <DropdownMenuLabel className="flex items-center justify-between">
-          <span>Notifications</span>
+          <span>{t("title.notifications")}</span>
           {unreadCount > 0 ? (
             <button
               type="button"
               onClick={handleMarkAllRead}
               className="text-primary text-xs hover:underline"
             >
-              <CheckCheck className="mr-1 inline h-3 w-3" />
-              Mark all read
+              <CheckCheck className="mr-1 inline h-3 w-3" aria-hidden="true" />
+              {t("actions.markAllRead")}
             </button>
           ) : null}
         </DropdownMenuLabel>
@@ -127,7 +129,7 @@ export function NotificationDropdown() {
         <ScrollArea className="max-h-[320px]">
           {notifications.length === 0 ? (
             <div className="text-muted-foreground px-4 py-8 text-center text-sm">
-              No notifications
+              {t("empty.noNotificationsDropdown")}
             </div>
           ) : (
             notifications.map((n) => {
@@ -144,12 +146,12 @@ export function NotificationDropdown() {
                   }}
                 >
                   <div className="bg-muted mt-0.5 flex size-7 shrink-0 items-center justify-center rounded-full">
-                    <Icon className="h-3.5 w-3.5" />
+                    <Icon className="h-3.5 w-3.5" aria-hidden="true" />
                   </div>
                   <div className="min-w-0 flex-1 space-y-0.5">
                     <div className="flex items-center gap-1.5">
                       {!n.isRead ? (
-                        <span className="bg-primary size-1.5 shrink-0 rounded-full" />
+                        <span className="bg-primary size-1.5 shrink-0 rounded-full" aria-hidden="true" />
                       ) : null}
                       <span className={cn("text-xs", !n.isRead ? "font-semibold" : "font-medium")}>
                         {n.title}
@@ -170,7 +172,7 @@ export function NotificationDropdown() {
         <DropdownMenuSeparator className="mt-0" />
         <DropdownMenuItem asChild>
           <Link href="/messages" className="text-primary justify-center text-xs">
-            View all notifications
+            {t("actions.viewAll")}
           </Link>
         </DropdownMenuItem>
       </DropdownMenuContent>