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 with
  extra_policies support and prometheus-metrics policy
- Update Promtail to use authenticated loki.home.2rjus.net endpoint
  only (remove unauthenticated monitoring01 client)
- Update pipe-to-loki and bootstrap to use loki.home.2rjus.net with
  basic auth from Vault secret
- Move migration plan to completed

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

hosts/monitoring02/configuration.nix

@@ -18,7 +18,7 @@
     role = "monitoring";
   };
 
-  homelab.dns.cnames = [ "grafana-test" "metrics" "vmalert" "loki" ];
+  homelab.dns.cnames = [ "monitoring" "alertmanager" "grafana" "grafana-test" "metrics" "vmalert" "loki" ];
 
   # Enable Vault integration
   vault.enable = true;

hosts/monitoring02/default.nix

@@ -4,5 +4,6 @@
     ../../services/grafana
     ../../services/victoriametrics
     ../../services/loki
+    ../../services/monitoring/alerttonotify.nix
   ];
 }