feat: 移植远程公告中心 (#9)

从 Axolotl 搬 RemoteAnnouncements.vue，顶栏加公告铃铛。远程拉取先禁用，等接口。

apps/app-frontend/src/helpers/remote-announcements.ts

@@ -64,3 +64,6 @@ export function isAnnouncementActive(item: RemoteAnnouncement, now = Date.now())
 export function announcementKey(item: RemoteAnnouncement) {
 	return item.id + ':' + item.published_at
 }
+
+export const REMOTE_ANNOUNCEMENTS_UPDATED_EVENT = 'starlight:remote-announcements-updated'
+export const OPEN_REMOTE_ANNOUNCEMENT_CENTER_EVENT = 'starlight:open-remote-announcement-center'