fix: switch containerd snapshotter from native to overlayfs

The 'native' snapshotter was a workaround for old cri-tools issues
(#436, #710) that are long resolved. It causes 'no unpack platforms
defined' errors with containerd v2.x. Switch to 'overlayfs' which
is kubespray's default and works correctly on ext4/xfs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Douglas Holt <dholt@nvidia.com>

Author: dholt

config.example/group_vars/k8s_cluster.yml

@@ -76,10 +76,9 @@ docker_registry_mirrors: "{{ groups['kube-master'] | map('regex_replace', '^(.*)
 #containerd_insecure_registries:
 #  "registry.local:31500": "http://registry.local:31500"
 
-# Workaround an issue where kubespray defaults are  causing containerd failures
-# https://github.com/kubernetes-sigs/cri-tools/issues/436
-# https://github.com/kubernetes-sigs/cri-tools/issues/710
-containerd_snapshotter: "native"
+# Use overlayfs snapshotter (kubespray default, works on ext4/xfs).
+# The previous "native" workaround for cri-tools #436/#710 is no longer needed.
+containerd_snapshotter: "overlayfs"
 
 # Work-around for https://github.com/kubernetes-sigs/kubespray/issues/8529
 nerdctl_extra_flags: " --insecure-registry"