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.

README.md

@@ -0,0 +1,83 @@
+# cachyos-gamescope-boot dev environment
+
+A QEMU/KVM test VM running CachyOS (KDE Plasma 6) for developing and testing
+[cachyos-gamescope-boot](https://github.com/theupriser/cachyos-gamescope-boot),
+plus helper scripts and a Claude Code skill that documents the test workflow.
+
+Only scripts and docs live here. The ISO, disk image, UEFI variable stores,
+logs and screenshots are generated locally. `.gitignore` is an allowlist: it
+ignores everything and un-ignores only the tracked files, so add any new
+tracked file to it explicitly.
+
+## Requirements
+
+- Linux host with KVM, `qemu-system-x86_64` (GTK/OpenGL display, virtfs/9p) and `qemu-img`
+  (Ubuntu: `sudo apt install qemu-system-x86 qemu-utils ovmf`).
+- OVMF firmware at `/usr/share/OVMF/OVMF_CODE_4M.fd` and `OVMF_VARS_4M.fd`.
+- `curl` and `sha256sum` for `get-iso.sh`.
+- Optional: an NVIDIA dGPU for `--nvidia` (PRIME offload of the virgl renderer).
+
+### Windows
+
+`run.ps1` and `get-iso.ps1` are Windows versions. They need
+[QEMU for Windows](https://qemu.weilnetz.de/w64/) (or set `QEMU_DIR`) and the
+"Windows Hypervisor Platform" feature (`-accel whpx`). Windows QEMU has no 9p
+shares: copy the repo into the guest with `scp -P 2222 -r ...`, and authorize
+your key with `.\add-ssh-key.ps1 -User <vm-user>`.
+
+## Quick start
+
+```bash
+./get-iso.sh        # download and verify the latest CachyOS desktop ISO
+./run.sh install    # first run creates disk.qcow2 (60G) and vars.fd, boots the ISO
+```
+
+Install CachyOS with the **KDE Plasma** desktop and **plasma-login-manager**
+as login manager. Power off and snapshot (only while the VM is off):
+
+```bash
+qemu-img snapshot -c clean disk.qcow2 && cp vars.fd vars.clean.fd
+```
+
+Boot the installed system (`./run.sh`) and, in the guest, enable SSH with key
+auth and passwordless sudo through the read-only `vmtools` share:
+
+```bash
+sudo mount -t 9p -o trans=virtio,version=9p2000.L vmtools /media && /media/guest-ssh-setup.sh
+```
+
+Power off and snapshot again:
+
+```bash
+qemu-img snapshot -c ssh-ready disk.qcow2 && cp vars.fd vars.ssh-ready.fd
+```
+
+Connect with `ssh -p 2222 <user>@localhost`. The project repo is shared
+read-write as 9p tag `repo`; in the guest:
+`sudo mount -t 9p -o trans=virtio,version=9p2000.L repo /mnt`.
+
+### run.sh options
+
+```
+[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; unstable)
+- `--fremont`: fake the Valve Steam Machine (Fremont) DMI data via `-smbios`
+- `REPO` defaults to `$HOME/projects/cachyos-gamescope-boot`
+
+## Helper scripts
+
+- `scripts/vmrun.sh '<menu input>'`: run the wizard in the guest's Plasma session with scripted input
+- `scripts/vmstate.sh`: print the state of every wizard component
+- `scripts/cmp.sh [save]`: save / diff the guest's KDE configs against a baseline
+
+They use `VM_USER` (default `theupriser`), `VM_PORT` (`2222`) and `VM_HOST` (`localhost`).
+
+## Claude Code skill
+
+The full test workflow is documented in
+[`.claude/skills/cachyos-vm-testing/SKILL.md`](.claude/skills/cachyos-vm-testing/SKILL.md);
+Claude Code picks it up when run from this repo.