ci: add workflow to validate PR description sections

[bearomorphism]

Description

Add a GitHub Actions workflow that validates PR descriptions contain the required sections from the PR template.

Required sections:

• Description
• Checklist
• Expected Behavior
• Steps to Test This Pull Request

Additional Context is intentionally optional.

Checklist

• I have read the contributing guidelines

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: GitHub Copilot following the guidelines

Code Changes

• Add test cases to all the changes you introduce
• Run uv run poe all locally to ensure this change passes linter check and tests
• Manually test the changes:
  • Verify the feature/bug fix works as expected in real-world scenarios
  • Test edge cases and error conditions
  • Ensure backward compatibility is maintained
  • Document any manual testing steps performed
• Update the documentation for the changes

Documentation Changes

N/A - CI workflow only.

Expected Behavior

PRs missing required description sections (Description, Checklist, Expected Behavior, Steps to Test) will fail the check with a clear message listing the missing sections.

Draft PRs and bot PRs (dependabot, renovate) are skipped.

Steps to Test This Pull Request

1. Open a PR with a properly filled template - check should pass
2. Open a PR with missing sections - check should fail listing the missing ones
3. Open a draft PR - check should be skipped

Additional Context

Validation results

• Positive test: PR with all sections → validate-pr passed ✅
• Negative test: PR body stripped to plain text → validate-pr failed ❌ with: PR description is missing required sections: Description, Checklist, Expected Behavior, Steps to Test This Pull Request

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.23%. Comparing base (efb1a7d) to head (89c7e92).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1947   +/-   ##
=======================================
  Coverage   98.23%   98.23%           
=======================================
  Files          61       61           
  Lines        2772     2772           
=======================================
  Hits         2723     2723           
  Misses         49       49           

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[Lee-W]

I'm ok with it but a bit not sure whehter rwe really need to enforce it this strict

[bearomorphism]

Maybe overkill. I just wanted to make sure everyone follows the contribution guideline.

[woile]

I think it's a bit too strict, a human may feel discouraged to fill everything, while an AI would read and fill everything.

I had some PR's where the template didn't apply (e.g: ci pr), and just filling it for the sake of filling, it feels like bureaucracy 😅

[bearomorphism]

Agree. Now a good enough AI should follow the guidelines. I already mention the docs in AGENTS.md.

Let's close this PR.