Cannot set only mqtt

If trying to set only mqtt, with

LOG_LEVEL=debug npx meross setup --ip 192.168.3.251 --mqtt mqtt://192.168.3.240

on a

mrs100 (hardware: 7.0.0, firmware: 7.6.19)

I get

```
2025-08-03 18:41:52 DEBUG: Transport initialized. Credentials: {"userId":0,"key":"meross"} {"name":"transport"}
2025-08-03 18:41:52 DEBUG: HTTPTransport initialized with URL: http://192.168.3.251/config {"name":"http"}
2025-08-03 18:41:52 DEBUG: Setting transport for device 00000000000000000000000000000000 to HTTPTransport {"name":"device","transport":{"id":"http://192.168.3.251/config","timeout":10000,"credentials":{"userId":0,"key":"meross"},"url":"http://192.168.3.251/config"}}
⠋Fetching device information…2025-08-03 18:41:52 INFO: Fetching device information for 00000000000000000000000000000000 {"name":"device"}
2025-08-03 18:41:52 DEBUG: Signing message edf334a8bb144ab3947dd1cd43b21c05 {}
2025-08-03 18:41:52 HTTP: POST http://192.168.3.251/config {} {"header":{"method":"GET","namespace":"Appliance.System.All","from":"http://192.168.3.251/config","messageId":"edf334a8bb144ab3947dd1cd43b21c05","timestamp":1754246513,"sign":"b2d78a7df1ed88a00651d89a28a0fd61"},"payload":{}} {"name":"request","requestId":"edf334a8bb144ab3947dd1cd43b21c05","request":{}}
2025-08-03 18:41:53 HTTP: 200 OK {} {"header":{"messageId":"edf334a8bb144ab3947dd1cd43b21c05","namespace":"Appliance.System.All","method":"ERROR","payloadVersion":1,"from":"/appliance/24121016765869700802c4e7ae1173cd/publish","uuid":"24121016765869700802c4e7ae1173cd","timestamp":1754246512,"timestampMs":184,"sign":"fb6bed2d662effde94f4e8ca28bf0e5c"},"payload":{"error":{"code":5001,"detail":"sign error"}}} {"name":"request","requestId":"edf334a8bb144ab3947dd1cd43b21c05","response":{}}
✗
Response was not GETACK
```