feat: replace markdown-link-check with lychee for link validation

[jeremyeder]

Summary

Replace markdown-link-check with lychee for faster, more reliable link validation in both local development and CI.

Changes

Link Checker Replacement

• Remove: markdown-link-check (Node.js-based, slower)
• Add: lychee v0.22.0 (Rust-based, faster, better maintained)

Configuration

• Created lychee.toml with smart exclusions:
  • Localhost URLs (http://localhost, http://127.0.0.1)
  • File protocol URLs (Jekyll-generated)
  • GitHub issue creation pages
  • Jinja2/Liquid template variables
  • Private/discussion pages

Pre-commit Hook

• Configured local pre-commit hook using absolute path to lychee binary
• Added ~/.cargo/bin to PATH for lychee availability
• Hook runs automatically before each commit on markdown/HTML files

GitHub Actions Workflow

• Created .github/workflows/link-check.yml
• Runs on:
  • Push to main and feature/** branches
  • All pull requests
  • Manual trigger via workflow_dispatch

Documentation Fixes

• Fixed git@ URLs → HTTPS in docs/_data/leaderboard.json
• Fixed Liquid template warnings in docs/developer-guide.md

Pre-commit Hook Updates

• Updated all pre-commit hooks to latest versions
• Removed deprecated markdown-link-check configuration

Benefits

Speed: Lychee is significantly faster than markdown-link-check
Reliability: Better maintained, active development
Dual Enforcement:

• Local: Fast feedback via pre-commit hook
• CI: Automatic enforcement via GitHub Actions

Testing

✅ Pre-commit hook tested locally
✅ Link checking verified on all markdown/HTML files
✅ GitHub Actions workflow syntax validated with actionlint

Files Changed

• .github/workflows/link-check.yml (new) - CI workflow
• .markdown-link-check.json (removed) - Old config
• .pre-commit-config.yaml (modified) - Updated hooks
• lychee.toml (new) - Lychee configuration
• docs/_data/leaderboard.json (modified) - Fixed git@ URLs
• docs/developer-guide.md (modified) - Fixed Liquid warnings
• docs/Gemfile (modified) - Added Ruby 3.4 compatibility gems

🤖 Generated with Claude Code

Co-Authored-By: Claude Sonnet 4.5 noreply@anthropic.com