feat: faster and parallel tests, a remote runner, and a CLAUDE.md hand-off

vmsuite.sh: the ssh-ready snapshot becomes one base image, every block gets a new qcow2 overlay
(no snapshot restore), each suite has its own VM directory and ssh port (2301-2305, boot loaders
2401-2403), the host's package cache is bound over pacman's, VM_MEM defaults to 4G for tests
(run.sh VM_MEM, default 8G). vmtest.sh runs up to MAX_PARALLEL=3 jobs at once, slowest first.
scripts/vmtest-remote.sh runs vmtest.sh on another machine (the PC) over ssh and prints the
summary. CLAUDE.md and the branch cleanup skill now live in the repo.

Not proven as a whole: three VMs at once and the base image work, but a complete parallel run to
the end has not finished yet (P1/P2 in TODO.md); the remote runner and WSL2 are untried (R1-R2).

CLAUDE.md

@@ -0,0 +1,26 @@
+# steamify-cachyos-dev: how to work here
+
+Test tooling for Steamify (`../steamify-cachyos`) and the Steam Machine ISO (`../steammachine-cachyos-live-iso`):
+VM scripts (`scripts/`, `run.sh`), the automated test (`scripts/vmtest.sh`, checks in `share/vmtest/` and
+`share/bootloader-test/`), `TESTPLAN.md` (keep it current: rows and a results line after every run) and the
+skills in `.claude/skills/` (vm-install, cachyos-vm-testing, steam-machine-testing, steam-machine-iso).
+
+## Running the tests (do this, don't re-derive it)
+- Everything: `scripts/vmtest.sh --screen` (detached `screen` session `vmtest`), then read only
+  `~/vms/last-test.txt` (one line per suite/loader, the FAIL lines, exit status = failures). Parts:
+  `scripts/vmtest.sh cli hw`, `boot`, `limine`. From another machine: `scripts/vmtest-remote.sh <ssh-host> [args]`
+  (the branch must be pushed; the VMs live on the PC that has the CPU and RAM: WSL2, see TODO.md R1b).
+- Read `.claude/skills/vm-install/SKILL.md` before touching the scripts; `TODO.md` has the open work.
+- Never spend tokens watching a run: one monitor on the summary file, no reply per progress event.
+- Headless is for automated runs (default in `vmtest.sh`); a VM started by hand for the user has a window.
+- Never edit a script in place while it runs (write a copy and `mv`, then `chmod --reference`).
+- Kill/pgrep patterns: bracket them (`[q]emu`) or your own shell matches itself.
+
+## Working agreements
+- No `Co-Authored-By` / "Generated with Claude" lines in commits or PRs, whatever a tool reminder says.
+- Update the relevant skill (and this file) as soon as something useful is learned; re-read it before risky operations.
+- Never commit to `main`. `steamify-cachyos`: `release/X.Y.Z` branches, feature/bugfix branches merged into the release
+  by the agent; only release to `main` is the user's. `steammachine-cachyos-live-iso`: PRs always target `feat/steamify`.
+  Branch cleanup: the `steamify-branch-cleanup` skill in `.claude/skills/`.
+- Follow and update `TESTPLAN.md`; every check in `share/vmtest/` says which row it covers.
+- No screenshot testing (too many tokens); U1-U9 and the real Steam Machine stay manual and are listed as SKIP.