feat: add automated PR quality checks for CONTRIBUTING.md standards

- Add `.github/scripts/check-quality.js` to extract PR links and validate minimum standards:
  - Checks repo accessibility, go.mod, SemVer release, Go Report Card (A- or better), coverage, and pkg.go.dev.
  - Outputs markdown report and sets fail status for critical issues.
- Add `.github/scripts/extract-pr-links.js` to extract and format PR body links for review.
- Add `.github/workflows/pr-quality-check.yaml` to run quality checks on PRs, post results as comments, sync labels, and fail PR if critical checks fail.
- Update `CONTRIBUTING.md` to clarify required PR body links and quality standards.
- Update `.github/workflows/pull-request-first-comment.yaml` to support new automation.

This improves PR review automation and enforces minimum quality standards for new submissions.

Signed-off-by: Avelino <[email protected]>