feat(scripts): recognize autolinks in check-links.py (Closes #2509)

[d-morrison]

Summary

Closes #2509.

Update scripts/check-links.py to recognize CommonMark autolinks (<https://...>, <mailto:...>, <user@example.com>) inside markdown table header cells (| <https://github.com> | Header 2 |), while skipping external targets and preserving link validation integrity.

Changes

• scripts/check-links.py:
  • Added AUTOLINK regex and extract_targets() helper.
  • Stripped standard inline links before scanning autolinks to prevent duplicate targets for pointy bracket link destinations ([text](<url>)).
  • Added bare email recognition to is_external().
  • Added check_target() helper with safe relative path formatting.
• scripts/test_check_links.py:
  • Added unit test suite covering table header autolinks, mailto autolinks, multiple autolinks in table cells, code fences/spans stripping, pointy bracket destinations, and valid/broken link handling.
• .github/workflows/validate.yml:
  • Registered scripts/test_check_links.py in CI workflow.

Verification

• python3 scripts/test_check_links.py (8 tests passed, 0 failed)
• python3 scripts/validate-skills.py (all skills and manifests valid)
• python3 scripts/check-links.py (2932 relative links across 642 markdown files verified, 0 broken)
• python3 scripts/check-test-suites-covered.py (all 45 test suites verified)
• npx --yes markdownlint-cli2@0.22.1 (0 errors across 711 files)
• Conducted adversarial self-review with clean verdict (Reviewed-Commit: 3a20741).

[d-morrison]

/review

[github-actions]

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[d-morrison]

Superseded by merged #2843 and #2839.