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/variables.tf

@@ -0,0 +1,16 @@
+variable "proxmox_endpoint" {
+  description = "URL of the Proxmox API endpoint, e.g. https://192.168.1.10:8006/"
+  type        = string
+}
+
+variable "proxmox_api_token" {
+  description = "Proxmox API token in the form user@realm!token-id=secret, e.g. terraform@pve!api-token-name=<SECRET>"
+  type        = string
+  sensitive   = true
+}
+
+variable "proxmox_insecure" {
+  description = "Skip TLS certificate verification (set true for self-signed certs)"
+  type        = bool
+  default     = true
+}