feat(vm_provision_mixin): expose fixed_vlan_tag for SDN vnets

vnet's SDN tag (VLAN ID) is now surfaced in get_network_targets() output
instead of being silently discarded. Bridges never set this field.

napalm_proxmox/vm_provision_mixin.py

@@ -415,6 +415,15 @@ class ProxmoxVMProvisionMixin:
             if not name:
                 continue
             # A vnet's VLAN is already fixed by its zone/tag — no separate vlan_tag applies.
-            targets.append({"name": name, "kind": "vnet", "vlan_aware": False})
+            tag = vnet.get("tag")
+            fixed_vlan_tag = int(tag) if tag is not None else None
+            targets.append(
+                {
+                    "name": name,
+                    "kind": "vnet",
+                    "vlan_aware": False,
+                    "fixed_vlan_tag": fixed_vlan_tag,
+                }
+            )
 
         return targets