quality pass and continuous integration #23

Goal

Make the checks that every pull request already passed run automatically on GitHub, and confirm the repository is clean.

Scope

• One GitHub Actions workflow: Python 3.12, install, ruff check, ruff format --check, pytest, on pushes to main and on pull requests
• Coverage used once as a diagnostic to look for untested rollback branches, not as a target
• Repository hygiene: no environment or cache files tracked, README defaults match the code

Acceptance criteria

• The workflow runs green on the pull request and on main
• pytest -q, ruff check . and ruff format --check . pass locally
• No untested failure or rollback branch found by the coverage diagnostic, or a test was added for it
• git status is clean after the merge

Validation

The green check mark on the pull request and on the main branch.