core: support mention notification

packages/ui-default/components/message/index.page.js

@@ -40,6 +40,12 @@ const messagePage = new AutoloadPage('messagePage', (pagename) => {
               <p>${i18n(msg.mdoc.content)}</p>
             </div>`,
         }).open();
+      } else if (msg.udoc._id === 1 && msg.mdoc.flag & 4) {
+        new VjNotification({
+          message: 'You received a system message, click here to view.',
+          duration: 15000,
+          action: () => window.open(`/home/messages?uid=${msg.udoc._id}`, '_blank'),
+        }).show();
       } else {
         // Is message
         new VjNotification({