Add SSE second-level dashboard stream and 2s client heartbeat.

Co-authored-by: Cursor <cursoragent@cursor.com>

desktop/gold_order_app.py

@@ -1447,23 +1447,22 @@ class OrderApp(tk.Tk):
         self._run_async(work)
 
     def _hub_heartbeat(self) -> None:
-        """定期 ping 中控，供网页显示在线；断线则提示（不允许离线运行）。"""
+        """约每 2 秒 ping 中控，供总览秒级在线状态。"""
+        interval_ms = 2000
         if hub_client is None or not is_activated():
-            self.after(60000, self._hub_heartbeat)
+            self.after(interval_ms, self._hub_heartbeat)
             return
 
         def work():
-            ok = False
             try:
-                ok = bool(hub_client.ping())
+                return bool(hub_client.ping())
             except Exception:
-                ok = False
-            return ok
+                return False
 
         def done(ok: bool):
             if not ok:
                 self.set_status("中控离线：请检查服务器，客户端需保持在线", ok=False)
-            self.after(60000, self._hub_heartbeat)
+            self.after(interval_ms, self._hub_heartbeat)
 
         def run():
             ok = work()