Implement HA control plane with Load Balancer (3-3 topology)

Major changes:
- Terraform: Scale to 3 control planes (cx23) + 3 workers (cx33)
- Terraform: Add Hetzner Load Balancer (lb11) for Kubernetes API
- Terraform: Add kube_api_lb_ip output
- Ansible: Add community.network collection to requirements
- Ansible: Update inventory to include LB endpoint
- Ansible: Configure secondary CPs and workers to join via LB
- Ansible: Add k3s_join_endpoint variable for HA joins
- Workflow: Add imports for cp-2, cp-3, and worker-3
- Docs: Update STABLE_BASELINE.md with HA topology and phase gates

Topology:
- 3 control planes (cx23 - 2 vCPU, 8GB RAM each)
- 3 workers (cx33 - 4 vCPU, 16GB RAM each)
- 1 Load Balancer (lb11) routing to all 3 control planes on port 6443
- Workers and secondary CPs join via LB endpoint for HA

Cost impact: +~€26/month (2 extra CPs + 1 extra worker + LB)

ansible/site.yml

@@ -73,6 +73,8 @@
     k3s_primary_ip: "{{ hostvars[groups['control_plane'][0]]['k3s_primary_private_ip'] }}"
     k3s_primary_public_ip: "{{ hostvars[groups['control_plane'][0]]['k3s_primary_public_ip'] }}"
     k3s_node_ip: "{{ k3s_private_ip }}"
+    # Use Load Balancer for HA - all control planes join via LB endpoint
+    k3s_join_endpoint: "{{ kube_api_endpoint | default(hostvars[groups['control_plane'][0]]['k3s_primary_private_ip']) }}"
 
   roles:
     - k3s-server
@@ -83,7 +85,8 @@
 
   vars:
     k3s_token: "{{ hostvars[groups['control_plane'][0]]['k3s_token'] }}"
-    k3s_server_url: "https://{{ hostvars[groups['control_plane'][0]]['k3s_primary_private_ip'] }}:6443"
+    # Use Load Balancer for HA - workers join via LB endpoint
+    k3s_server_url: "https://{{ kube_api_endpoint | default(hostvars[groups['control_plane'][0]]['k3s_primary_private_ip']) }}:6443"
     k3s_node_ip: "{{ k3s_private_ip }}"
 
   roles: