feat(textlint): gate hard-wrapped Markdown prose

[shunk031]

Summary

This adds a shared chezmoi-managed textlint configuration and a repository-local Node pre-commit hook that autofixes hard-wrapped Markdown prose. The deterministic document review invokes the same rules with JSON output, reports quoted findings, and fails when textlint is unavailable or returns a fatal error. The seven salvaged fixtures preserve the exact unwrap result, blockquote skip behavior, and document-global spacing behavior. Please review and approve the shared configuration, hook behavior, and fixture-preserving changes.

Validation

• uv run --python 3.14.6 --no-project python -m unittest discover -s tests/python -p 'test_*.py' (94 tests passed)
• OAI_API_KEY=true prek run textlint-markdown --files .tmp-textlint-validation.md (passed and fixed the disposable hard wrap)
• Direct textlint checks from a different working directory matched unwrap_expected.txt, preserved blockquote_expected.txt, and matched spacing_side_effect_expected.txt byte-for-byte.

Research basis

• The pre-commit local-hook documentation supports repo: local, language: node, and pinned additional_dependencies without a custom mirror.
• The textlint CLI documentation documents --fix, --format json, --config, and fatal exit status handling.
• The no-arbitrary-line-break implementation confirms the autofix and default blockquote-skip behavior used here.