fix(ci): use Terraform provider for ISO upload, fix port/lockfile issues

- Use proxmox_virtual_environment_file resource to upload the auto-install
  ISO via the API. terraform destroy now cleans up both the VM and ISO.
- Remove manual upload-to-pve.sh and cleanup-pve-storage.sh scripts.
- Commit .terraform.lock.hcl for reproducible CI builds.
- Replace iso_file_id variable with iso_local_path and iso_storage.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/infrastructure/variables.tf

@@ -56,11 +56,17 @@ variable "disk_storage" {
   default     = "nas-iscsi-lvm"
 }
 
-variable "iso_file_id" {
-  description = "Proxmox file ID of the auto-install PVE ISO (e.g. local:iso/proxmox-ve_9.1-1-auto.iso)"
+variable "iso_local_path" {
+  description = "Local path to the prepared auto-install PVE ISO on the runner"
   type        = string
 }
 
+variable "iso_storage" {
+  description = "Proxmox storage pool for uploading the ISO (must accept ISO content type)"
+  type        = string
+  default     = "local"
+}
+
 variable "network_bridge" {
   description = "Network bridge on the host to attach the nested PVE VM to"
   type        = string