homelab: add deploy.enable option with assertion

- Add homelab.deploy.enable option (requires vault.enable)
- Create shared homelab-deploy Vault policy for all hosts
- Enable homelab.deploy on all vault-enabled hosts

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

hosts/vaulttest01/configuration.nix

@@ -92,6 +92,7 @@ in
   # Testing config
   # Enable Vault secrets management
   vault.enable = true;
+  homelab.deploy.enable = true;
 
   # Define a test secret
   vault.secrets.test-service = {