fix: keep DHCP enabled by default on template VM

The template machine can lose connectivity when rebuilt directly because it has no cloud-init network data during template maintenance. Restore DHCP as the default for the template itself while keeping cloud-init + networkd enabled so cloned VMs can still consume injected network settings.

nixos/template-base/configuration.nix

@@ -10,7 +10,7 @@ in
       ./hardware-configuration.nix;
 
   networking.hostName = "k8s-base-template";
-  networking.useDHCP = false;
+  networking.useDHCP = lib.mkDefault true;
   networking.useNetworkd = true;
   networking.nameservers = [ "1.1.1.1" "8.8.8.8" ];