UniFi Express can report type 'udm' instead of 'ux' in the API,
causing get_gateway_info() to return it as the gateway instead of
the actual dedicated gateway (e.g. UDM Pro) when both are present.
Now checks model code (UX, UXBSDM) in addition to device type to
correctly identify Express devices and treat them as fallback-only.

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