[AI Generated]: refactor(*): 保活定时器与连接清理逻辑收口至 app.js，修复 null 安全与注释错误

- 新增 app.startKeepAlive/stopKeepAlive/cleanupConnection，bus 监听自动控制保活与断联清理
- Blue.stop() 收入 cleanupConnection，页面 onHide/onUnload 统一调用
- 修复 replaceNetwork.js seviceList 可能为 undefined 导致崩溃
- 修复 configureDevice_2.js device.mac 为 null 时崩溃
- 修复 replaceNetwork_1.js activeProtocol 无 null 检查及 wifiList 容错
- 修正 configureDevice_4.js 超时注释（3分钟→30秒）

app.js

@@ -151,6 +151,42 @@ App({
 		this.globalData.ppScale.plugin = requirePlugin('ppScale-plugin');
 	},
 
+	// 保活定时器引用
+	_keepAliveTimer: null,
+
+	/**
+	 * 启动保活定时器，每 15 秒发送一次保活指令
+	 * 内部已做去重处理，重复调用安全
+	 */
+	startKeepAlive() {
+		this.stopKeepAlive();
+		this._keepAliveTimer = setInterval(() => {
+			if (this.globalData.ppScale.activeProtocol) {
+				this.globalData.ppScale.activeProtocol.sendKeepAliveCode();
+			}
+		}, 15000);
+	},
+
+	/**
+	 * 清除保活定时器
+	 */
+	stopKeepAlive() {
+		if (this._keepAliveTimer) {
+			clearInterval(this._keepAliveTimer);
+			this._keepAliveTimer = null;
+		}
+	},
+
+	/**
+	 * 页面离开时的统一清理：停止保活 + 重置重连计数 + connectState 置空 + 停止蓝牙
+	 */
+	cleanupConnection() {
+		this.stopKeepAlive();
+		this.resetReconnectCount();
+		this.setGlobalData('ppScale.device.connectState', null);
+		this.globalData.ppScale.plugin.Blue.stop();
+	},
+
 	/**
 	 * 注册全局 bus 事件监听（connectState / syncDeviceTimeSuccess / deviceWillDisconnect）
 	 * 依赖 Blue.stop() 清空订阅，onShow 时直接调用，无需标志位
@@ -164,8 +200,10 @@ App({
 			this.setGlobalData('ppScale.device.connectState', res);
 			if (res == plugin.BLUE_STATE.CONNECTSUCCESS) {
 				this.globalData.ppScale.reconnect.count = 0;
+				this.startKeepAlive();
 			}
 			if (res == plugin.BLUE_STATE.CONNECTFAILED) {
+				this.stopKeepAlive();
 				this.reconnectDevice();
 			}
 			wx.hideLoading();
@@ -179,6 +217,7 @@ App({
 		// 设备自动断开监听
 		plugin.bus.subscribe('deviceWillDisconnect', (res) => {
 			console.log("app.js ===> deviceWillDisconnect", res);
+			this.stopKeepAlive();
 			this.setGlobalData('ppScale.device.connectState', plugin.BLUE_STATE.CONNECTFAILED);
 		});
 	},