fix: prevent kubelet auto-start during rebuild

Add wantedBy = [] to prevent kubelet from being started by multi-user.target
during nixos-rebuild switch. This allows rebuilds to succeed even when the
cluster is in a transitional state. Kubelet will be started by kubeadm
init/join commands instead.

nixos/kubeadm/modules/k8s-common.nix

@@ -227,6 +227,7 @@ in
 
   systemd.services.kubelet = {
     description = "Kubernetes Kubelet";
+    wantedBy = lib.mkForce [];
     wants = [ "network-online.target" ];
     after = [ "containerd.service" "network-online.target" ];
     unitConfig.ConditionPathExists = "/var/lib/kubelet/config.yaml";