nix-cache02: add homelab-deploy builder service

- Configure builder to build nixos-servers and nixos (gunter) repos
- Add builder NKey to Vault secrets
- Update NATS permissions for builder, test-deployer, and admin-deployer
- Grant nix-cache02 access to shared homelab-deploy secrets

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

hosts/nix-cache02/builder.nix

@@ -0,0 +1,44 @@
+{ config, ... }:
+{
+  # Fetch builder NKey from Vault
+  vault.secrets.builder-nkey = {
+    secretPath = "shared/homelab-deploy/builder-nkey";
+    extractKey = "nkey";
+    outputDir = "/run/secrets/builder-nkey";
+    services = [ "homelab-deploy-builder" ];
+  };
+
+  # Configure the builder service
+  services.homelab-deploy.builder = {
+    enable = true;
+    natsUrl = "nats://nats1.home.2rjus.net:4222";
+    nkeyFile = "/run/secrets/builder-nkey";
+
+    settings.repos = {
+      nixos-servers = {
+        url = "git+https://git.t-juice.club/torjus/nixos-servers.git";
+        defaultBranch = "master";
+      };
+      nixos = {
+        url = "git+https://git.t-juice.club/torjus/nixos.git";
+        defaultBranch = "master";
+      };
+    };
+
+    metrics.enable = true;
+  };
+
+  # Expose builder metrics for Prometheus scraping
+  homelab.monitoring.scrapeTargets = [
+    {
+      job_name = "homelab-deploy-builder";
+      port = 9973;
+    }
+  ];
+
+  # Ensure builder starts after vault secret is available
+  systemd.services.homelab-deploy-builder = {
+    after = [ "vault-secret-builder-nkey.service" ];
+    requires = [ "vault-secret-builder-nkey.service" ];
+  };
+}

hosts/nix-cache02/default.nix

@@ -1,5 +1,6 @@
 { ... }: {
   imports = [
     ./configuration.nix
+    ./builder.nix
   ];
 }