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)

terraform/variables.tf

@@ -25,7 +25,7 @@ variable "cluster_name" {
 variable "control_plane_count" {
   description = "Number of control plane nodes"
   type        = number
-  default     = 1
+  default     = 3
 }
 
 variable "control_plane_type" {
@@ -37,7 +37,7 @@ variable "control_plane_type" {
 variable "worker_count" {
   description = "Number of worker nodes"
   type        = number
-  default     = 2
+  default     = 3
 }
 
 variable "worker_type" {