Migrate CI linting from pre-commit to prek #150

Summary

Follow-up from #149 (which touched .github/workflows/pre-commit.yml). Migrate the linting CI from pre-commit to prek — a fast Git-hook manager written in Rust, designed as a drop-in alternative to pre-commit.

Why

• Faster — several times quicker than pre-commit in CI.
• No Python runtime needed — prek is a single self-contained binary, so the actions/setup-python + pip install pre-commit steps go away.
• Compatible — it reads the existing .pre-commit-config.yaml and runs the same hooks (prettier, editorconfig-checker, actionlint), and also supports a native prek.toml.
• Less disk usage; shared toolchain installs across hooks.

Scope / checklist

• Convert the config to prek's native format:

  prek util yaml-to-toml   # .pre-commit-config.yaml -> prek.toml

  ⚠️ YAML comments are not preserved during conversion. Our current .pre-commit-config.yaml has no comments, so nothing is lost — but re-add any if some are introduced before the migration lands.
• Decide the fate of .pre-commit-config.yaml:
  • Replace it with prek.toml (cleanest), or
  • keep both if we still want contributors to be able to run plain pre-commit locally. Note pre-commit cannot read prek.toml, so going toml-only means local hook runs require prek.
• Update .github/workflows/pre-commit.yml to use the official action (drop setup-python + pip install):

  - uses: actions/checkout@v4
  - uses: j178/prek-action@v2

• Confirm all three hooks still run and pass under prek (prettier, editorconfig-checker, actionlint).
• Update contributor docs / README to mention prek install / prek run --all-files.
• Optional: pin prek-action to a commit SHA to match the repo's other pinned actions.

References

• prek: https://github.com/j178/prek
• prek docs: https://prek.j178.dev/
• prek GitHub Action: https://github.com/j178/prek-action

Tooling/CI chore — not a pipeline/RFC/SIG proposal, so it is intentionally outside the approval-automation flow.