feat: add bare bones Proxmox Terraform scaffold

Adds provider config, variables, and an example tfvars file using
the bpg/proxmox provider. No resources are managed yet — existing
Proxmox setup is untouched.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

variables.tf

@@ -0,0 +1,21 @@
+variable "proxmox_endpoint" {
+  description = "URL of the Proxmox API endpoint, e.g. https://192.168.1.10:8006/"
+  type        = string
+}
+
+variable "proxmox_username" {
+  description = "Proxmox user in the form user@realm, e.g. terraform@pve"
+  type        = string
+}
+
+variable "proxmox_password" {
+  description = "Password for the Proxmox user"
+  type        = string
+  sensitive   = true
+}
+
+variable "proxmox_insecure" {
+  description = "Skip TLS certificate verification (set true for self-signed certs)"
+  type        = bool
+  default     = true
+}