fix: expose OpenClaw CLI to gateway-spawned agent shells

[szymo]

Problem

AlphaClaw starts with /app/node_modules/.bin on PATH, but gateway-spawned agent shells can receive a minimal PATH without that directory. openclaw then fails with exit 127 even though the bundled package and Gateway are healthy. Agents may fall back to stale paths such as /app/openclaw.mjs, producing MODULE_NOT_FOUND.

Fix

• Resolve the installed OpenClaw package entrypoint without assuming npm hoisting layout.
• Atomically install or refresh /usr/local/bin/openclaw during AlphaClaw startup.
• Preserve an unmanaged regular launcher.
• Verify the launcher with openclaw --version and emit a clear warning if setup fails.
• Document the launcher behavior.

Validation

• npm test: 732 passed; one unrelated existing failure in openclaw-codex-migration.test.js (SQLite verification does not find imported profile).
• Focused startup/Gateway suite: 54 passed.
• New runtime helper suite: 5 passed.
• Real deployment reproduction: isolated OpenClaw cron executed openclaw --version with exit 0 after the launcher was present.

The startup operation is idempotent and refreshes stale symlinks after package updates.