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/layout.tsx

@@ -13,6 +13,7 @@ import PostLinkProvider from "@/components/PostLinkProvider";
 import CodeFoldProvider from "@/components/markdown/CodeFoldProvider";
 import MotionProvider from "@/components/MotionProvider";
 import CommentsPolicyProvider from "@/components/CommentsPolicyProvider";
+import MessagesPolicyProvider from "@/components/MessagesPolicyProvider";
 import type { User } from "@/lib/api";
 import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
 import { TOKEN_COOKIE, authCookieHeader } from "@/lib/cookies";
@@ -121,24 +122,26 @@ export default async function RootLayout({
         </a>
         <MotionProvider initial={motionCfg}>
           <CommentsPolicyProvider allowComments={settings.allow_comments !== false}>
-            <PostLinkProvider openInNewTab={settings.post_link_new_tab !== false}>
-              <CodeFoldProvider
-                initialEnabled={settings.code_block_auto_fold}
-                initialFoldLines={settings.code_block_fold_lines}
-              >
-                <SiteChrome
-                  initialIsAdmin={isAdmin}
-                  user={user}
-                  unread={unread}
-                  chatUnread={chatUnread}
-                  theme={theme}
-                  siteName={settings.site_name}
-                  allowRegister={settings.allow_register}
+            <MessagesPolicyProvider allowMessages={settings.allow_messages !== false}>
+              <PostLinkProvider openInNewTab={settings.post_link_new_tab !== false}>
+                <CodeFoldProvider
+                  initialEnabled={settings.code_block_auto_fold}
+                  initialFoldLines={settings.code_block_fold_lines}
                 >
-                  {children}
-                </SiteChrome>
-              </CodeFoldProvider>
-            </PostLinkProvider>
+                  <SiteChrome
+                    initialIsAdmin={isAdmin}
+                    user={user}
+                    unread={unread}
+                    chatUnread={settings.allow_messages !== false ? chatUnread : 0}
+                    theme={theme}
+                    siteName={settings.site_name}
+                    allowRegister={settings.allow_register}
+                  >
+                    {children}
+                  </SiteChrome>
+                </CodeFoldProvider>
+              </PostLinkProvider>
+            </MessagesPolicyProvider>
           </CommentsPolicyProvider>
         </MotionProvider>
         <Toaster />