fix: stabilize kubeadm bootstrap and reduce Proxmox plan latency

Move kubeadm reset ahead of kube-vip manifest generation, use super-admin.conf during bootstrap for kube-vip, and restore admin.conf after init. Also switch nixos-rebuild to --sudo and make QEMU guest agent optional so Terraform plan can skip slow guest-agent refreshes when it is not installed.

terraform/variables.tf

@@ -99,6 +99,12 @@ variable "pm_api_url" {
   type = string
 }
 
+variable "qemu_agent_enabled" {
+  type        = bool
+  default     = false
+  description = "Enable QEMU guest agent integration in Proxmox resources"
+}
+
 variable "SSH_KEY_PUBLIC" {
   type        = string
   description = "Public SSH key injected via cloud-init"