Add ruff + black checks to CI

[Fiyiware]

Context

CONTRIBUTING.md states that the project formats with black (default config) and lints with ruff (default config), but notes CI does not enforce them yet. This issue closes that gap.

What to do

• Add black --check and ruff check steps to the GitHub Actions workflow, scoped to prototype/.
• Add black and ruff to the dev dependencies.
• Run black and ruff --fix once over prototype/ and commit the formatting pass in a separate commit from the CI change, so the CI commit is reviewable on its own.

Acceptance criteria

• CI fails if code is not black-formatted or has ruff errors.
• The existing prototype code passes both checks after the initial formatting pass.
• CONTRIBUTING.md updated to say the checks are now enforced.

Good to know

Use default configs for both tools (no custom rule tweaking in this PR). If ruff flags something that needs a real code change rather than autofix, leave it and mention it in the PR description.