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/skills/steamify-branch-cleanup/SKILL.md

@@ -0,0 +1,22 @@
+---
+name: steamify-branch-cleanup
+description: Clean up git branches in steamify-cachyos (and sibling steamify repos) following the release-branch flow. Use when the user asks to clean up / prune branches.
+---
+
+# Steamify branch cleanup
+
+Rules:
+- ALWAYS keep `main` and every `release/X.Y.Z` branch (local and remote). Never delete them.
+- Delete `feature/*` and `bugfix/*` branches (local and remote) only when merged into `origin/main` or the current `origin/release/*` branch.
+- Delete local branches whose remote is gone (`[origin/...: gone]`) only if they are `feature/*` or `bugfix/*`; local stale `release/*` branches are kept unless the user says otherwise.
+- Never touch unmerged branches; list them and report instead.
+- Never commit or merge to main.
+
+Steps:
+1. `git fetch --all --tags --prune`
+2. `git checkout main && git merge --ff-only origin/main`
+3. List candidates: `git branch -vv`, `git branch -r --merged origin/main`, and same for the current release branch.
+4. Delete local (`git branch -d`) and remote (`git push origin --delete <b>`) feature/bugfix branches per the rules above.
+5. Report what was deleted and what was kept.
+
+Note: remote deletions may be blocked by the auto-mode classifier; if so, stop and let the user approve a permission rule or run it via `!`.