fix(k3s-server): harden isolated control-plane bootstrap

- pin kube-vip and cluster traffic to the private guest interface\n- disable disposable guest firewalls and verify API reachability before joins\n- keep control-plane orchestration on the primary and preserve failure diagnostics

molecule/single_node/overrides.yml

@@ -7,6 +7,7 @@
         # See:
         # https://github.com/flannel-io/flannel/blob/67d603aaf45ef80f5dd39f43714fc5e6f8a637eb/Documentation/troubleshooting.md#Vagrant
         flannel_iface: eth1
+        kube_vip_iface: eth1
 
         # The test VMs might be a bit slow, so we give them more time to join the cluster:
         retry_count: 45