feat: active user count

src/lib/stores/index.ts

@@ -15,6 +15,7 @@ export const MODEL_DOWNLOAD_POOL = writable({});
 export const mobile = writable(false);
 
 export const socket: Writable<null | Socket> = writable(null);
+export const activeUserCount: Writable<null | number> = writable(null);
 
 export const theme = writable('system');
 export const chatId = writable('');