homelab-deploy: enable prometheus metrics

- Update homelab-deploy input to get metrics support
- Enable metrics endpoint on port 9972
- Add scrape target for prometheus auto-discovery

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

system/homelab-deploy.nix

@@ -19,8 +19,15 @@ in
       natsUrl = "nats://nats1.home.2rjus.net:4222";
       nkeyFile = "/run/secrets/homelab-deploy-nkey";
       flakeUrl = "git+https://git.t-juice.club/torjus/nixos-servers.git";
+      metrics.enable = true;
     };
 
+    # Expose metrics for Prometheus scraping
+    homelab.monitoring.scrapeTargets = [{
+      job_name = "homelab-deploy";
+      port = 9972;
+    }];
+
     # Ensure listener starts after vault secret is available
     systemd.services.homelab-deploy-listener = {
       after = [ "vault-secret-homelab-deploy-nkey.service" ];