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>

terraform/vault/hosts-generated.tf

@@ -36,6 +36,7 @@ locals {
     "nix-cache02" = {
       paths = [
         "secret/data/hosts/nix-cache02/*",
+        "secret/data/shared/homelab-deploy/*",
       ]
     }