fix(mqtt): MQTT 连接成功后自动周期上报心跳（绑定页/主屏通用）

- mqtt.js：connect 后立即+每10s 上报 opc/display/heartbeat（client_id/tenant_id/page），
  绑定页(BindScreen)不再只连不报——admin 端屏幕管理即可看到在线大屏；
  断线 close 时清定时器，重连后自动恢复
- useMqttControl.js：移除重复心跳（避免双发），保留注册/状态上报/订阅逻辑

src/utils/mqtt.js

@@ -1,23 +1,42 @@
 import { useState, useEffect } from 'react';
 import mqtt from 'mqtt';
-import { getMqttUrl, getMqttCredentials, getDeviceId, MQTT_TOPIC_COMMAND, MQTT_TOPIC_TICK, MQTT_TOPIC_BIND } from '../config';
+import { getMqttUrl, getMqttCredentials, getDeviceId, MQTT_TOPIC_COMMAND, MQTT_TOPIC_TICK, MQTT_TOPIC_BIND, MQTT_TOPIC_HEARTBEAT } from '../config';
 import { getTenantId } from './tenant';
 
 /* =========================================================
    MQTT 客户端（mqtt.js）—— 后端控制通道
    订阅 opc/display/command（页面/媒体/卡片控制）与 opc/dashboard/tick（数据快照）
+   连接成功后自动周期上报心跳 opc/display/heartbeat（绑定页/主屏通用，
+   后端据此统计在线大屏，admin 端屏幕管理显示在线状态）
    断线自动重连；未连接时静默降级（页面仍可本地操作）
    ========================================================= */
 
+const HEARTBEAT_MS = 10000;
+
 let client = null;
 let status = 'connecting'; // connecting | connected | offline
 let clientId = null;
+let heartbeatTimer = null;
 const listeners = new Set();
 
 function notifyStatus() {
   window.dispatchEvent(new CustomEvent('dpm:mqtt-status', { detail: { status } }));
 }
 
+/** 心跳上报（连接成功后自动周期调用；绑定页/主屏均生效） */
+function sendHeartbeat() {
+  if (status !== 'connected' || !client) return;
+  try {
+    const page = (typeof window !== 'undefined' && window.location) ? window.location.pathname : '';
+    client.publish(MQTT_TOPIC_HEARTBEAT, JSON.stringify({
+      client_id: getClientId() || getDeviceId(),
+      tenant_id: getTenantId(),
+      page,
+      ts: Date.now(),
+    }), { qos: 1 });
+  } catch { /* 忽略单次失败 */ }
+}
+
 /* 每个连接生成全局唯一 client_id（独立客户端 ID 铁律）：
    优先 crypto.randomUUID（WebView2/现代浏览器），回退时间戳+双段高熵随机 */
 function makeClientId() {
@@ -55,6 +74,11 @@ export function connectMqtt() {
         tid ? `${MQTT_TOPIC_TICK}/${tid}` : MQTT_TOPIC_TICK,
         tid ? `${MQTT_TOPIC_COMMAND}/${tid}/${clientId}` : `${MQTT_TOPIC_COMMAND}/${clientId}`,
       ], { qos: 1 });
+      // 连接成功即启动心跳（绑定页/主屏通用；幂等防重复定时器）
+      if (!heartbeatTimer) {
+        sendHeartbeat();
+        heartbeatTimer = setInterval(sendHeartbeat, HEARTBEAT_MS);
+      }
     });
     client.on('reconnect', () => {
       status = 'connecting';
@@ -63,6 +87,7 @@ export function connectMqtt() {
     client.on('close', () => {
       status = 'offline';
       notifyStatus();
+      if (heartbeatTimer) { clearInterval(heartbeatTimer); heartbeatTimer = null; }
     });
     client.on('error', () => {
       status = 'offline';

src/utils/useMqttControl.js

@@ -1,7 +1,7 @@
 import { useEffect } from 'react';
 import { useNavigate, useLocation } from 'react-router-dom';
 import { onMqttMessage, connectMqtt, publishMqtt, getClientId, useMqttStatus } from './mqtt';
-import { MQTT_TOPIC_HEARTBEAT, MQTT_TOPIC_COMMAND, MQTT_TOPIC_BIND, getApiBase as API_BASE } from '../config';
+import { MQTT_TOPIC_COMMAND, MQTT_TOPIC_BIND, getApiBase as API_BASE } from '../config';
 import { getTenantId, clearBinding } from './tenant';
 import { Sfx } from './sounds';
 import { PAGE_ORDER } from './pageNav';
@@ -75,23 +75,7 @@ export function useMqttControl() {
     return off;
   }, []);
 
-  // 大屏在线心跳（后端据此统计在线大屏数）
-  useEffect(() => {
-    connectMqtt();
-    const sendHeartbeat = () => {
-      if (mqttStatus === 'connected') {
-        publishMqtt(MQTT_TOPIC_HEARTBEAT, {
-          client_id: getClientId(),
-          tenant_id: getTenantId(),
-          page: location.pathname,
-          ts: Date.now(),
-        });
-      }
-    };
-    sendHeartbeat();
-    const hb = setInterval(sendHeartbeat, 10000);
-    return () => clearInterval(hb);
-  }, [mqttStatus, location.pathname]);
+  // 大屏在线心跳已由 mqtt.js 连接成功后自动周期上报（绑定页/主屏通用），此处不再重复发送
 
   // 页面状态即时上报：路由变化即通知服务端当前所在页面
   useEffect(() => {