monitoring02: add Caddy reverse proxy for VictoriaMetrics and vmalert

Add metrics.home.2rjus.net and vmalert.home.2rjus.net CNAMEs with
Caddy TLS termination via internal ACME CA.

Refactors Grafana's Caddy config from configFile to globalConfig +
virtualHosts so both modules can contribute routes to the same
Caddy instance.

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

hosts/monitoring02/configuration.nix

@@ -18,8 +18,7 @@
     role = "monitoring";
   };
 
-  # DNS CNAME for Grafana test instance
-  homelab.dns.cnames = [ "grafana-test" ];
+  homelab.dns.cnames = [ "grafana-test" "metrics" "vmalert" ];
 
   # Enable Vault integration
   vault.enable = true;