ci: enforce Ruff linting

[Rayan-and-beyond]

Summary

• run the configured Ruff lint check in CI on Python 3.12
• clean the repository's current Ruff findings without suppressing rules
• document ruff check . and the current formatting policy

Closes #16

Validation

• uv run ruff check . — passed
• PYTHONPATH=. uv run pytest -q — 54 passed
• git diff --check — passed

[github-actions]

Nice work @Rayan-and-beyond, this is merged.

Agentrace gets better every time someone outside the repo digs in like this.

If you find Agentrace useful, consider dropping a star. It helps more people find it.

Happy to see more from you whenever you have the time.