fix: upload one ISO per PVE version, not per node

Changed Terraform ISO resource from for_each=pve_instances (per-node)
to for_each=pve_isos (per-version). With HTTP answer server, both
nodes of the same version share the same generic ISO.

New pve_isos variable maps version to ISO path. pve_instances now
has pve_version field instead of iso_local_path. VMs reference
their version's ISO via auto_iso[each.value.pve_version].

Updated run-integration.sh tfvars generation and -target flags
for both provision and cleanup to use the new schema.

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

tests/infrastructure/variables.tf

@@ -21,15 +21,21 @@ variable "target_node" {
 }
 
 variable "pve_instances" {
-  description = "Map of PVE instances to provision. Key is a label (e.g. 'pve9'), value defines the VM."
+  description = "Map of PVE instances to provision. Key is a node label (e.g. '9a'), value defines the VM."
   type = map(object({
-    iso_local_path = string
-    vm_id          = number
-    vm_name        = string
-    mac_address    = string
+    pve_version = string
+    vm_id       = number
+    vm_name     = string
+    mac_address = string
   }))
 }
 
+variable "pve_isos" {
+  description = "Map of PVE version to the local path of the generic HTTP auto-install ISO."
+  type        = map(string)
+  default     = {}
+}
+
 variable "cores" {
   description = "Number of CPU cores to allocate to each nested PVE VM"
   type        = number