refactor: restructure repo into environments/modules layout

Separates nonprod into its own working directory for independent
state isolation. Follows HashiCorp guidance on environment separation.

environments/nonprod/terraform.tfvars.example

@@ -0,0 +1,6 @@
+# Copy this file to terraform.tfvars and fill in your values.
+# terraform.tfvars is gitignored to keep secrets out of version control.
+
+proxmox_endpoint = "https://192.168.1.10:8006/"
+proxmox_api_token = "terraform@pve!terraform-nonprod=<secret>"
+proxmox_insecure = true