monitoring02: add Caddy reverse proxy for VictoriaMetrics and vmalert

Add metrics.home.2rjus.net and vmalert.home.2rjus.net CNAMEs with
Caddy TLS termination via internal ACME CA.

Refactors Grafana's Caddy config from configFile to globalConfig +
virtualHosts so both modules can contribute routes to the same
Caddy instance.

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

services/grafana/default.nix

@@ -87,22 +87,20 @@
   services.caddy = {
     enable = true;
     package = pkgs.unstable.caddy;
-    configFile = pkgs.writeText "Caddyfile" ''
-      {
-        acme_ca https://vault.home.2rjus.net:8200/v1/pki_int/acme/directory
-        metrics
-      }
-
-      grafana-test.home.2rjus.net {
-        log {
-          output file /var/log/caddy/grafana.log {
-            mode 644
-          }
+    globalConfig = ''
+      acme_ca https://vault.home.2rjus.net:8200/v1/pki_int/acme/directory
+      metrics
+    '';
+    virtualHosts."grafana-test.home.2rjus.net".extraConfig = ''
+      log {
+        output file /var/log/caddy/grafana.log {
+          mode 644
         }
-
-        reverse_proxy http://127.0.0.1:3000
       }
-
+      reverse_proxy http://127.0.0.1:3000
+    '';
+    # Metrics endpoint on plain HTTP for Prometheus scraping
+    extraConfig = ''
       http://${config.networking.hostName}.home.2rjus.net/metrics {
         metrics
       }