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>

terraform/vault/hosts-generated.tf

@@ -44,7 +44,16 @@ locals {
         "secret/data/hosts/garage01/*",
       ]
     }
-  
+    "monitoring02" = {
+      paths = [
+        "secret/data/hosts/monitoring02/*",
+        "secret/data/hosts/monitoring01/apiary-token",
+        "secret/data/services/grafana/*",
+        "secret/data/shared/nats/nkey",
+      ]
+      extra_policies = ["prometheus-metrics"]
+    }
+
   }
 
   # Placeholder secrets - user should add actual secrets manually or via tofu
@@ -74,7 +83,10 @@ resource "vault_approle_auth_backend_role" "generated_hosts" {
 
   backend            = vault_auth_backend.approle.path
   role_name          = each.key
-  token_policies     = ["host-${each.key}", "homelab-deploy", "nixos-exporter", "loki-push"]
+  token_policies     = concat(
+    ["host-${each.key}", "homelab-deploy", "nixos-exporter", "loki-push"],
+    lookup(each.value, "extra_policies", [])
+  )
   secret_id_ttl      = 0 # Never expire (wrapped tokens provide time limit)
   token_ttl          = 3600
   token_max_ttl      = 3600