Fix cloud IP fallback and off-state attrs

[ejc3]

Summary

This fixes two local-control issues used by the Home Assistant AiDot integration:

• Fix send_dev_attr() when setting attributes while the light is off. The method attempted to add OnOff to an undefined variable named attr; it should mutate the supplied dev_attr payload.
• Use the cloud-reported properties.ipAddress as a fallback when UDP discovery has not provided an IP, while keeping UDP discovery authoritative when it succeeds.
• Expose a read-only ip_address property so integrations do not need to read _ip_address directly.

Details

DeviceClient.send_dev_attr() currently raises NameError for calls such as brightness/color/CCT while the device is off, because the code uses attr[CONF_ON_OFF] instead of dev_attr[CONF_ON_OFF].

AidotClient.get_device_client() now reads properties.ipAddress defensively only when properties is a dict. If UDP discovery has a current IP, that still wins. If not, the cloud IP is used as a best-effort LAN fallback, including when the previous IP is disconnected.

Validation

• py_compile passes for aidot/client.py, aidot/device_client.py, and aidot/models/device_client_model.py.
• git diff --check passes.
• Companion Home Assistant AiDot draft PR: Apply all supplied turn_on attributes hass-AiDot#30