chore: add CONTRIBUTING.md

Author: t-timms

CONTRIBUTING.md

@@ -0,0 +1,16 @@
+# Contributing
+
+1. Fork the repo
+2. Create a feature branch (`git checkout -b feature/amazing-feature`)
+3. Install dev dependencies: `pip install -r requirements.txt`
+4. Make changes with tests
+5. Run checks: `ruff check . --fix && ruff format . && pytest`
+6. Commit with conventional format: `feat(scope): description`
+7. Push and open a PR
+
+## Code Standards
+
+- Type hints on all public functions
+- `ruff` for linting and formatting
+- `pytest` for testing
+- No `print()` — use `logging.getLogger(__name__)`