fix(openclaw): stop stamping stale version, add --no-always opt-out

[pierrz]

Problem

Found while integrating caveman into an OpenClaw deployment and reading bin/lib/openclaw.js:

1. Stale version stamp. SKILL_VERSION = '1.0.0' is hardcoded and gets written into every installed skill's frontmatter regardless of the actual release — currently v1.9.1. openclaw skills list reports a version that's never been accurate since the constant was introduced.
2. No opt-out for always-on. installOpenclaw() unconditionally stamps always: true and writes the SOUL.md bootstrap block. There's no flag to install caveman as a discoverable, load-on-demand skill only (which the module's own top-of-file comment describes as a supported mode — "Skills there... are loaded on-demand by the model" — but nothing in the installer actually lets you land in that mode).

Fix

Both scoped narrowly, no default-behavior change:

• Version: mergeOpenclawFrontmatter() / installOpenclaw() accept an explicit version override. bin/install.js's --only openclaw path now passes PINNED_REF (already bumped on every release for hook-integrity pinning — this reuses that existing, maintained value instead of introducing a second version source). SKILL_VERSION stays as the fallback for callers that don't pass one explicitly.
• --no-always: new flag. Skips the always: true frontmatter stamp and the SOUL.md write; only the skill file is installed. Re-running --no-always over an already always-on install does not retroactively strip the existing SOUL.md block — it only changes what a new install does (covered by a test).

Before / after

- version: 1.0.0
+ version: 1.9.1

# new: install caveman for OpenClaw without forcing always-on
npx -y github:JuliusBrussee/caveman -- --only openclaw --no-always

Tests

4 new cases in tests/installer/e2e.freshinstall.test.mjs:

• version threading (CAVEMAN_REF override → frontmatter reflects it, not the fallback)
• --no-always: skill written, versioned, no always: key, SOUL.md not created
• --no-always idempotency: doesn't strip a SOUL.md block from a prior always-on install

Existing openclaw suite (always-on default, idempotent re-run, uninstall, marker damage-tolerance from #596) is unmodified and still green — confirms the default install path is unchanged.

npm test: 113/115 pass locally, including all 4 new tests. The 2 failures are pre-existing — they reproduce on an unmodified checkout of main in this sandbox, caused by a real claude CLI + ~/.openclaw present in the environment (tests documented as "skipped without claude CLI" detect it and take a different path). Unrelated to this change; not touched here.

Scope note

src/tools/caveman-init.js (the per-repo rule-file installer) also calls helper.installOpenclaw() for its openclaw target, and is left unchanged — it's a differently-scoped tool (drops rule files for many editors into a target repo, explicitly documented as installing an "always-on caveman rule") and extending it is a separate concern per the one-PR-one-concern guidance in CONTRIBUTING.md. Happy to follow up there if useful.