refactor(display): tie VFD display to WS connection state only

Made-with: Cursor

lib/client.js

@@ -131,6 +131,7 @@ class ClawClient {
       this._backoff = 1_000;
       this._sendConnect();
       this._startPing();
+      led.display.showTime(); // 连上云端 → 显示时间
     });
 
     ws.on('message', (data) => {
@@ -150,6 +151,7 @@ class ClawClient {
       this._clearPing();
       if (!this._stopped) {
         log.warn('clawd', `连接断开 (${code})，${this._backoff / 1000}s 后重连...`);
+        led.display.showAP(); // 断开云端 → 显示 AP
         setTimeout(() => this._connect(), this._backoff);
         this._backoff = Math.min(this._backoff * 2, MAX_BACKOFF_MS);
       }