ENH: switch to prek

[redeboer]

Closes #694

⚙️ Enhancements

• Replaced pre-commit with prek, a drop-in replacement that reads the same .pre-commit-config.yaml file. The check-dev-files hook now updates CONTRIBUTING.md instructions, the _upgrade-precommit Poe/Pixi task, and removes pre-commit, pre-commit-uv, and prek from dependency groups.
• The generated _upgrade-precommit task now runs prek autoupdate without the -j flag, since prek does not support it.
• Added a .prekignore file so the test fixture under tests/utilities/precommit/ is not treated as a nested prek project.

🐛 Bug fixes

• Kept the field ordering of the generated _upgrade-uv Poe task consistent (cmd before executor), so regenerating it no longer produces spurious diff noise.

🔨 Maintenance

• Removed the now-redundant .gitignore exceptions for files that are already tracked.

📝 Documentation

• Unwrapped hard-wrapped Markdown paragraphs under docs/.

Squash commit messages

* DOC: unwrap hard-wrapped Markdown under docs
* ENH: run `prek autoupdate` without `-j` flag
* FIX: keep upgrade task field ordering consistent
* MAINT: remove redundant `.gitignore` exceptions