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.ps1

@@ -0,0 +1,29 @@
+# CachyOS test VM for setup-gamescope-boot.sh -- Windows version.
+#   .\run.ps1 [-Install]
+# Needs QEMU for Windows (https://qemu.weilnetz.de/w64/) and the Windows
+# feature "Windows Hypervisor Platform" (for -accel whpx).
+# Windows QEMU has no 9p shared folders: copy the repo in over SSH instead:
+#   scp -P 2222 -r ..\..\projects\cachyos-gamescope-boot <user>@localhost:
+param([switch]$Install)
+$ErrorActionPreference = 'Stop'
+Set-Location $PSScriptRoot
+
+$qemuDir = if ($env:QEMU_DIR) { $env:QEMU_DIR } else { 'C:\Program Files\qemu' }
+$qemu = Join-Path $qemuDir 'qemu-system-x86_64.exe'
+$code = Join-Path $qemuDir 'share\edk2-x86_64-code.fd'
+
+if (-not (Test-Path vars.fd)) { Copy-Item (Join-Path $qemuDir 'share\edk2-i386-vars.fd') vars.fd }
+if (-not (Test-Path disk.qcow2)) { & (Join-Path $qemuDir 'qemu-img.exe') create -f qcow2 disk.qcow2 60G | Out-Null }
+
+$qargs = @(
+    '-accel', 'whpx,kernel-irqchip=off', '-machine', 'q35', '-cpu', 'max', '-smp', '6', '-m', '8G',
+    '-drive', "if=pflash,format=raw,readonly=on,file=$code",
+    '-drive', 'if=pflash,format=raw,file=vars.fd',
+    '-drive', 'file=disk.qcow2,if=virtio',
+    '-device', 'virtio-vga,xres=1920,yres=1080', '-display', 'sdl',
+    '-device', 'qemu-xhci', '-device', 'usb-tablet',
+    '-nic', 'user,model=virtio-net-pci,hostfwd=tcp::2222-:22'
+)
+if ($Install) { $qargs += @('-cdrom', 'cachyos.iso', '-boot', 'd') }
+
+& $qemu @qargs