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
- Update migration plan with current status

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

hosts/http-proxy/configuration.nix

@@ -18,9 +18,6 @@
     "sonarr"
     "ha"
     "z2m"
-    "grafana"
-    "prometheus"
-    "alertmanager"
     "jelly"
     "pyroscope"
     "pushgw"