fix: remove kubeconfig references, use try() for pod runtime files

- main.tf: remove kubeconfig_path local (no longer used with direct auth)
- providers.tf: wrap file() with try() to handle plan-time on non-pod systems

try() allows terraform plan to work locally; at runtime in pod, files exist and are used.

terraform/main.tf

@@ -1,6 +1,5 @@
 locals {
-  kubeconfig_path = var.kubeconfig_path
-  cluster_domain  = var.cluster_domain
+  cluster_domain = var.cluster_domain
 }
 
 # Helm repositories will be created in helm-repositories.tf