fix: Add CachyOS test VM dev environment and VM testing skill

QEMU/KVM scripts for a CachyOS KDE test VM (run.sh/run.ps1, get-iso,
guest SSH setup), host helper scripts to drive and inspect the
cachyos-gamescope-boot wizard in the guest, and a Claude Code skill
documenting the test workflow.

run.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+# CachyOS test VM for setup-gamescope-boot.sh.
+#   [REPO=/path/to/cachyos-gamescope-boot] ./run.sh [install] [--nvidia] [--vulkan] [--fremont]
+#     install    boot the installer ISO
+#     --nvidia   render the guest's virtio-gpu (virgl) on the host NVIDIA dGPU
+#     --vulkan   expose Vulkan to the guest (venus; needed by gamescope, can be unstable)
+#     --fremont  report the Valve Steam Machine's DMI data (for testing the wizard)
+# REPO defaults to $HOME/projects/cachyos-gamescope-boot.
+# The repo is shared into the guest; mount it there with:
+#   sudo mount -t 9p -o trans=virtio,version=9p2000.L repo /mnt
+# First-time SSH setup, inside the guest:
+#   sudo mount -t 9p -o trans=virtio,version=9p2000.L vmtools /media && /media/guest-ssh-setup.sh
+# SSH from the host: ssh -p 2222 <user>@localhost
+cd "$(dirname "$0")"
+repo="${REPO:-$HOME/projects/cachyos-gamescope-boot}"
+
+cdrom=()
+smbios=()
+gpu=virtio-vga-gl,xres=1920,yres=1080
+for arg in "$@"; do
+    case "$arg" in
+        install)  cdrom=(-cdrom cachyos.iso -boot d) ;;
+        --nvidia) export __NV_PRIME_RENDER_OFFLOAD=1 __GLX_VENDOR_LIBRARY_NAME=nvidia \
+                         __EGL_VENDOR_LIBRARY_FILENAMES=/usr/share/glvnd/egl_vendor.d/10_nvidia.json ;;
+        --vulkan) gpu+=,hostmem=4G,blob=true,venus=true ;;
+        --fremont) smbios=(-smbios type=1,manufacturer=Valve,product=Fremont -smbios type=2,manufacturer=Valve,product=Fremont) ;;
+        *) echo "unknown argument: $arg" >&2; exit 1 ;;
+    esac
+done
+
+# First run: create the disk and the writable UEFI variable store.
+[[ -f disk.qcow2 ]] || qemu-img create -f qcow2 disk.qcow2 60G
+[[ -f vars.fd ]] || cp /usr/share/OVMF/OVMF_VARS_4M.fd vars.fd
+
+# Hand the host's public keys to the guest setup script.
+cat ~/.ssh/*.pub > share/host-keys.pub
+
+exec qemu-system-x86_64 \
+    -enable-kvm -machine q35,memory-backend=mem -cpu host -smp 6 -m 8G \
+    -object memory-backend-memfd,id=mem,size=8G,share=on \
+    -drive if=pflash,format=raw,readonly=on,file=/usr/share/OVMF/OVMF_CODE_4M.fd \
+    -drive if=pflash,format=raw,file=vars.fd \
+    -drive file=disk.qcow2,if=virtio \
+    -device "$gpu" -display gtk,gl=on,zoom-to-fit=off \
+    -device qemu-xhci -device usb-tablet \
+    -nic user,model=virtio-net-pci,hostfwd=tcp::2222-:22 \
+    -virtfs local,path="$repo",mount_tag=repo,security_model=mapped-xattr \
+    -virtfs local,path="$PWD/share",mount_tag=vmtools,security_model=mapped-xattr,readonly=on \
+    "${smbios[@]}" "${cdrom[@]}"