docs(ego-browser): guard skill helper contract

[tt-a1i]

Summary

Make the current Playwright-style keyboard surface explicit in the canonical ego-browser Skill and prevent executable examples from drifting back to removed global helpers. Also ensure changes to the canonical Skill trigger the repository quality-gates workflow.

This is the repository-side portion of #260. The hosted documentation examples still need to be updated in their publishing source.

Related issue

Related to #260

Changes

• Document the current page.keyboard and locator keyboard methods in skills/ego-browser/SKILL.md.
• Add a regression test that scans executable Skill examples for unqualified calls to removed global helpers.
• Reuse the runtime's legacy-helper list as the test's source of truth.
• Run quality gates when the canonical Skill changes, not only when site learnings change.

Verification

npm test                         # 312 passed
npm run validate:site-skills     # passed
npm run validate:agent-style     # passed
npm run typecheck                # passed
npm audit --audit-level=moderate # 0 vulnerabilities
prettier --check                 # passed for changed package files
git diff --check                 # passed

A real-browser E2E run passed 43/45 cases (518 assertions), including helper surface, Task Spaces, and both keyboard suites. Two unrelated environment/flaky cases failed:

• screencast recording: the Ego subprocess could not find FFmpeg, although it is installed at /opt/homebrew/bin/ffmpeg on the host;
• concert ticket rush: inventory remained 2 instead of decrementing to 1.

Impact

• Public helper API or behavior
• Agent skill or instructions
• Site learning
• Installation or update flow
• Build, CI, or release process
• Documentation only
• No externally visible impact

No runtime helper behavior changes. The test only guards examples against APIs already removed on dev.

Checklist

• The PR targets the correct base branch (dev for normal changes; only dev may target main).
• The change is focused and does not include unrelated cleanup.
• Tests were added or updated for behavior changes, or the reason they are unnecessary is explained above.
• Relevant tests and validation commands pass locally.
• Public helper JSDoc and agent-facing documentation are updated when the helper surface changes.
• No credentials, tokens, cookies, personal data, or other secrets are included.
• A release-note label is selected (feat, fix, docs, chore, ci, or refactor). The repository currently exposes none of these labels, so documentation was applied instead.