fix(iot-gateway): 修正RPC环境变量名不匹配导致连接失败

docker-compose中VIEWSH_IOT_GATEWAY_RPC_URL与yaml期望的VIEWSH_GATEWAY_RPC_URL不一致，
导致iot-gateway回退到默认值127.0.0.1:48091，容器间无法通信。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

viewsh-module-iot/viewsh-module-iot-gateway/src/main/resources/application-prod.yaml

@@ -36,7 +36,7 @@ viewsh:
     gateway:
       # 设备 RPC 配置
       rpc:
-        url: ${VIEWSH_GATEWAY_RPC_URL:http://127.0.0.1:48091}
+        url: ${VIEWSH_GATEWAY_RPC_URL:http://aiot-iot-server:48091}
         connect-timeout: ${VIEWSH_RPC_CONNECT_TIMEOUT:30s}
         read-timeout: ${VIEWSH_RPC_READ_TIMEOUT:30s}
       # 设备 Token 配置