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)
- Add shared/nats/nkey to monitoring02 Vault AppRole policy

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

services/grafana/default.nix

@@ -91,6 +91,14 @@
       acme_ca https://vault.home.2rjus.net:8200/v1/pki_int/acme/directory
       metrics
     '';
+    virtualHosts."grafana.home.2rjus.net".extraConfig = ''
+      log {
+        output file /var/log/caddy/grafana.log {
+          mode 644
+        }
+      }
+      reverse_proxy http://127.0.0.1:3000
+    '';
     virtualHosts."grafana-test.home.2rjus.net".extraConfig = ''
       log {
         output file /var/log/caddy/grafana.log {