The TP-Link gateway was wired via ExternalName `gw.viktorbarzin.lan`, but
Technitium has no record for that name (the router isn't a DHCP client and
Kea DDNS never registers it), so the ingress backend returned NXDOMAIN and
the `[External] gw` Uptime Kuma monitor was permanently failing.
Factory now accepts `backend_ip` as an alternative to `external_name`: it
creates a selector-less ClusterIP Service + manual EndpointSlice pointing
at the given IP, bypassing cluster DNS entirely. Used for gw (192.168.1.1);
the old ExternalName path is retained for every other service.
Also add a direct `port` monitor for the router in uptime-kuma's
internal_monitors list so we can tell a Cloudflare/tunnel outage apart
from the router itself being down. Extended the internal-monitor-sync
script to handle non-DB monitor types (hostname + port fields).
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