feat: 后台增加开放消息开关

关闭后前台隐藏私聊/群聊入口并由后端拦截；同步去掉公告页重复计数胶囊。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/chat/[id]/page.tsx

@@ -2,10 +2,11 @@ import type { Metadata } from "next";
 import { notFound, redirect } from "next/navigation";
 import { cookies } from "next/headers";
 import { authCookieHeader } from "@/lib/cookies";
-import { getMeCached } from "@/lib/serverData";
+import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
 import { fetchChatRoom, fetchChatMessages, fetchChatRooms } from "@/lib/api";
 import ChatShell from "../ChatShell";
 import ChatRoomClient from "./ChatRoomClient";
+import MessagesUnsupported from "@/components/MessagesUnsupported";
 
 interface PageProps {
   params: Promise<{ id: string }>;
@@ -13,6 +14,9 @@ interface PageProps {
 
 export async function generateMetadata({ params }: PageProps): Promise<Metadata> {
   const { id } = await params;
+  if ((await getPublicSettingsCached()).allow_messages === false) {
+    return { title: "本站不支持消息" };
+  }
   try {
     const { room } = await fetchChatRoom(id, authCookieHeader(await cookies()));
     const title =
@@ -27,6 +31,9 @@ export async function generateMetadata({ params }: PageProps): Promise<Metadata>
 
 export default async function ChatRoomPage({ params }: PageProps) {
   const { id } = await params;
+  if ((await getPublicSettingsCached()).allow_messages === false) {
+    return <MessagesUnsupported />;
+  }
   const cookie = authCookieHeader(await cookies());
   const me = await getMeCached(cookie || undefined);
   if (!me.user) {