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/app/(dashboard)/messages/compose/page.tsx

@@ -1,3 +1,6 @@
+import type { Metadata } from "next"
+import type { JSX } from "react"
+import { getTranslations } from "next-intl/server"
 import { requirePermission } from "@/shared/lib/auth-guard"
 import { Permissions } from "@/shared/types/permissions"
 import { getRecipients } from "@/modules/messaging/data-access"
@@ -5,17 +8,22 @@ import { MessageCompose } from "@/modules/messaging/components/message-compose"
 
 export const dynamic = "force-dynamic"
 
-export const metadata = {
-  title: "Compose Message",
+export async function generateMetadata(): Promise<Metadata> {
+  const t = await getTranslations("messages")
+  return {
+    title: t("title.compose"),
+    description: t("description.compose"),
+  }
 }
 
 export default async function ComposeMessagePage({
   searchParams,
 }: {
   searchParams: Promise<{ parentId?: string; receiverId?: string; subject?: string }>
-}) {
+}): Promise<JSX.Element> {
   const ctx = await requirePermission(Permissions.MESSAGE_SEND)
   const sp = await searchParams
+  const t = await getTranslations("messages")
 
   const recipients = await getRecipients(ctx.userId, ctx.dataScope)
 
@@ -23,8 +31,8 @@ export default async function ComposeMessagePage({
     <div className="flex h-full flex-col p-8">
       <div className="mx-auto w-full max-w-3xl space-y-6">
         <div>
-          <h2 className="text-2xl font-bold tracking-tight">Compose Message</h2>
-          <p className="text-muted-foreground">Send a message to another user.</p>
+          <h2 className="text-2xl font-bold tracking-tight">{t("title.compose")}</h2>
+          <p className="text-muted-foreground">{t("description.compose")}</p>
         </div>
         <MessageCompose
           recipients={recipients}