feat(k3s): replace nginx loadbalancer with kube-vip for control-plane HA

Deploys kube-vip as a DaemonSet on all k3s server nodes, advertising a
VIP (192.168.20.2) via ARP. Eliminates the single-point-of-failure
k3s-loadbalancer VM.

- New kube_vip role: RBAC + DaemonSet templates, TLS SAN cert rotation
- playbooks/kube-vip.yaml: migration playbook (serial=1, idempotent)
- Updated k3s install tasks (server primary/secondary, agent) to use k3s_vip
  instead of the loadbalancer VM IP
- Added k3s_vip: 192.168.20.2 to group_vars (below DHCP range .11-.250)

Migration steps in playbook header comment.

vars/group_vars/k3s/vars.yaml

@@ -2,6 +2,8 @@ k3s:
   loadbalancer:
     default_port: 6443
 
+k3s_vip: "192.168.20.2"
+
 k3s_primary_server_ip: "{{ groups['k3s_server'] | map('extract', hostvars, 'ansible_default_ipv4') | map(attribute='address') | unique | list | first }}"
 k3s_server_ips: "{{ groups['k3s_server'] | map('extract', hostvars, 'ansible_default_ipv4') | map(attribute='address') | unique | list }}"