Provisions prom.w5isp.com (10.0.15.31) as the home-cluster monitoring host.
Prometheus 3.6.0 scrapes the Talos cluster API/nodes/cAdvisor via an external
SA token; Grafana ships with the Prometheus datasource pre-provisioned.
host_vars opens 9090/9093/9100/3000 to 10.0.0.0/16 plus SSH from the home LAN
so the firewall role doesn't lock out admin access.
