ci: use markdown-link-check action in tests workflow

[blink1073]

References

Description

Replaces the manual-stage markdown-link-check pre-commit hook with the reusable calysto/maintainer_tools/actions/markdown-link-check@v1 action, run as a dedicated job in the tests workflow.

Changes

• Add a markdown_link_check job to .github/workflows/tests.yml using calysto/maintainer_tools/actions/markdown-link-check@v1, and add it to tests_check.needs.
• Remove the tcort/markdown-link-check pre-commit hook.
• Delete .markdown_link_config.json; the action's bundled defaults cover the previous settings. The generated metakernel/magics/README.md (which contains fake example URLs from magic docstrings) is skipped via the action's ignore-paths input.

Backwards-incompatible changes

None

Testing

• actionlint passes on the modified workflow.
• Ran markdown-link-check locally against the whole repo using the action's default config plus the new ignore-paths value; exit 0.

AI usage

• Some or all of the content of this PR was generated by AI.
• The human author has carefully reviewed this PR and run this code.
• AI tools and models used: opencode (deepseek-v4p1-flash)

[greptile-apps]

Confidence Score: 4/5

[Medium impact] Moves markdown link checking from local tool to CI workflow.

The PR appears safe to merge, with a non-blocking update needed to the local link-check instructions.

Findings

1.  Local link-check instructions are stale ▶

Summary

Moves Markdown link checks from a manual pre-commit hook to a dedicated CI job.

• Markdown link checks run as part of the test workflow.

_{Reviews (1) · Last reviewed commit: "ci: use markdown-link-check action in te..." · Reviewed by Greptile}

[greptile-apps]

Local link-check instructions are stale

CONTRIBUTING.md still tells contributors that just lint-all runs markdown-link-check, but this removes that hook. The command no longer checks links locally. Update the contributor instructions and the comment above lint-all in justfile to explain that link checks now run in CI.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.56%. Comparing base (750dd4f) to head (8a44974).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #499   +/-   ##
=======================================
  Coverage   93.56%   93.56%           
=======================================
  Files          51       51           
  Lines        2982     2982           
  Branches      414      414           
=======================================
  Hits         2790     2790           
  Misses        129      129           
  Partials       63       63           

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