Improve LAN device identity detection

[Corsair-cxs]

Summary

• enrich host names from DNS, getent, Avahi/mDNS, and SSDP/UPnP discovery
• preserve multiple IPs for the same MAC address during scans
• show a fallback label for unnamed hosts in the device table

Motivation

Some LAN devices expose useful identity data through mDNS or SSDP but do not have PTR records, so the Name column could stay empty.

Also, devices with multiple interfaces or ARP flux can appear as the same MAC on multiple IPs. The previous scan map used MAC as the only key, so one IP could overwrite the other.

Changes

• add host identity enrichment helpers
• match scan results by MAC+IP before falling back to MAC-only matching
• avoid MAC-only fallback when an existing host is already known on multiple IPs
• add tests for same-MAC multi-IP scan behavior
• add frontend fallback display for unnamed hosts

Testing

• go test ./...
• verified locally with a device exposing two LAN IPs