terraform: fix cloud-init conditional type inconsistency

Fix OpenTofu error where static IP and DHCP branches had different object
structures in the subnets array. Move conditional to network_config level
so both branches return complete, consistent yamlencode() results.

Error was: "The true and false result expressions must have consistent types"

Solution: Make network_config itself conditional rather than the subnets
array, ensuring both branches return the same type (string from yamlencode).

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

terraform/cloud-init.tf

@@ -25,27 +25,34 @@ resource "proxmox_cloud_init_disk" "ci" {
 : ""}
   EOT
 
-# Network configuration - static IP or DHCP
+  # Network configuration - static IP or DHCP
-network_config = yamlencode({
+  network_config = each.value.ip != null ? yamlencode({
     version = 1
     config = [{
       type = "physical"
       name = "ens18"
-    subnets = each.value.ip != null ? [{
+      subnets = [{
         type            = "static"
         address         = each.value.ip
         gateway         = each.value.gateway
         dns_nameservers = split(" ", each.value.nameservers)
         dns_search      = [each.value.search_domain]
-      }] : [{
+      }]
+    }]
+    }) : yamlencode({
+    version = 1
+    config = [{
+      type = "physical"
+      name = "ens18"
+      subnets = [{
         type = "dhcp"
       }]
     }]
-})
+  })
 
-# Instance metadata
+  # Instance metadata
-meta_data = yamlencode({
+  meta_data = yamlencode({
     instance_id    = sha1(each.key)
     local-hostname = each.key
-})
+  })
 }