Use ruff format for Markdown when format_tool=ruff

[tsvikas]

Summary

• When the ruff formatter is selected, drop blacken-docs entirely and use ruff format (preview) to format Python code blocks inside Markdown files. Feature added in ruff 0.15.0.
• The Black variant keeps using blacken-docs.

Changes

• project_name/pyproject.toml.jinja: enable [tool.ruff.format].preview = true and [tool.ruff].extend-include = ["*.md"] so ruff format discovers and formats Markdown files; drop black from dev deps when not using Black.
• project_name/.pre-commit-config.yaml.jinja: drop the blacken-docs and black-pre-commit-mirror hooks for the ruff variant; add types_or: [python, pyi, jupyter, markdown] to ruff-format.
• project_name/justfile.jinja: drop blacken-docs from the format recipe and _sync-blacken-docs from deps-update for the ruff variant; gate the _sync-blacken-docs recipe behind format_tool == "black".
• ctt.toml: ignore PC111 (sp-repo-review requirement to use blacken-docs) since ruff format replaces it for the ruff variant.
• README.md, CONTRIBUTING.md.jinja: document the new behavior.

Test plan

• CI passes for both Black and Ruff variants in ctt
• ruff format reformats Python code blocks inside *.md files in the ruff variant
• ruff check skips *.md files (lint not affected)
• blacken-docs still present and runs for the Black variant

[sourcery-ai]

Hey - I've reviewed your changes and they look great!

---

Sourcery is free for open source - if you like our reviews please consider sharing them ✨

• X
• Mastodon
• LinkedIn
• Facebook

_{Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.}