monitoring02: enable alerting and migrate CNAMEs from http-proxy

- Switch vmalert from blackhole mode to sending alerts to local
  Alertmanager
- Import alerttonotify service so alerts route to NATS notifications
- Move alertmanager and grafana CNAMEs from http-proxy to monitoring02
- Add monitoring CNAME to monitoring02
- Add Caddy reverse proxy entries for alertmanager and grafana
- Remove prometheus, alertmanager, and grafana Caddy entries from
  http-proxy (now served directly by monitoring02)
- Move monitoring02 Vault AppRole to hosts-generated.tf and add
  shared/nats/nkey access

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

terraform/vault/approle.tf

@@ -115,15 +115,6 @@ locals {
       ]
     }
 
-    # monitoring02: Grafana + VictoriaMetrics
-    "monitoring02" = {
-      paths = [
-        "secret/data/hosts/monitoring02/*",
-        "secret/data/hosts/monitoring01/apiary-token",
-        "secret/data/services/grafana/*",
-      ]
-    }
-
   }
 }