Add public contribution templates

[jang1563]

Summary

• add CONTRIBUTING.md with benchmark-submission and public-release contribution guidance
• add issue forms for data/docs, reproducibility, and benchmark submission discussions
• add a pull request template with release QA and public-surface checks
• link the contribution guide and submission format from the README
• extend public docs validation to require the contribution links

Verification

• make release-qa
• make hpc-public-qa
• python3 -m unittest tests/test_review_fixes.py
• YAML parse check for .github/ISSUE_TEMPLATE/*.yml
• git diff --check origin/main..HEAD