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.

.gitignore

@@ -0,0 +1,27 @@
+# Allowlist: ignore everything, then un-ignore only scripts and docs.
+# New tracked files must be added here explicitly.
+/*
+!/.gitignore
+!/README.md
+!/run.sh
+!/run.ps1
+!/get-iso.sh
+!/get-iso.ps1
+!/add-ssh-key.ps1
+!/scripts/
+!/share/
+!/.claude/
+
+share/*
+!share/guest-ssh-setup.sh
+
+# Belt and braces, anywhere in the tree
+*.iso
+*.iso.version
+*.qcow2
+*.img
+*.fd
+*.png
+*.log
+*.tmp
+host-keys.pub