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/monitoring01/configuration.nix

@@ -58,6 +58,7 @@
 
   # Vault secrets management
   vault.enable = true;
+  homelab.deploy.enable = true;
   vault.secrets.backup-helper = {
     secretPath = "shared/backup/password";
     extractKey = "password";