Add GitHub PR issue triage domain skill

[HCVincent]

Summary

• Add a GitHub PR/Issue triage domain skill for public repository contribution review.
• Document API-first workflows for open PR shortlists, PR details, changed files, issue duplicate checks, review comments, and check-runs.
• Add a focused unit test to keep the new skill's required sections and API paths covered.

Verification

• git diff --check
• uv --directory . run --with pytest python -m pytest tests/unit/test_github_domain_skills.py -q
• uv --directory . run python -m compileall src tests
• Manually verified the documented workflow against browser-use/browser-harness with browser-harness, including PR list, PR detail, changed files, and check-runs.

Notes

• Local full unit suite on Windows still reports three pre-existing failures unrelated to this PR: two Snap symlink path assertions and the packaged SKILL.md symlink assertion.

---

Summary by cubic

Adds a GitHub PR/Issue triage domain skill with API‑first workflows and a quick triage rubric, incorporating review feedback to make duplicate checks and CI status clearer. Adds tests to lock in required sections, endpoints, and edge‑case guidance.

• New Features
  • Added agent-workspace/domain-skills/github/pr-issue-triage.md covering PR shortlist (/pulls), PR detail and files (/pulls/{n} and /pulls/{n}/files), issue duplicate checks (/issues and search), review comments, and CI checks via /commits/{head_sha}/check-runs, with rate-limit notes, pagination, browser verification tips, and a “Quick triage rubric”.
  • Added unit tests to verify required headings and core API paths, and to assert reviewed edge cases (search query syntax, docs_or_skill_only, checks_green using completed runs).

^{Written for commit e1d0991. Summary will update on new commits.}

[cubic-dev-ai]

3 issues found across 2 files

<sub>Reply with feedback, questions, or to request a fix.

Fix all with cubic | Re-trigger cubic</sub>