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.

roles/k3s_agent/tasks/installation.yaml

@@ -24,6 +24,6 @@
   ansible.builtin.command: |
     /tmp/k3s_install.sh
   environment:
-    K3S_URL: "https://{{ hostvars['k3s-loadbalancer'].ansible_default_ipv4.address }}:{{ k3s.loadbalancer.default_port }}"
+    K3S_URL: "https://{{ k3s_vip }}:{{ k3s.loadbalancer.default_port }}"
     K3S_TOKEN: "{{ k3s_token }}"
   become: true