Add CachyOS VM creation script

Introduce an interactive script (vm/cachyos-vm.sh) to create and configure a CachyOS VM on Proxmox. The script validates Proxmox environment and architecture, offers default and advanced settings via whiptail, detects storage/ISO locations, downloads the CachyOS desktop ISO, allocates EFI and main disks, creates and configures the VM (network, CPU, memory, disks, boot order, OVMF), sets a rich VM description, and optionally starts the VM. Also add an ASCII header file (vm/headers/cachyos-vm) used by the script.

Author: MickLesk