- Add guess_the_number package with set_difficulty, check_answer and
play_game, plus constants.py (range, attempts, ASCII logo)
- Add pytest tests for difficulty, feedback and full game flow
- Add pyproject.toml (Python >= 3.13, no runtime dependencies)
- Add docs/Doxyfile and Doxygen comments in the source
- Rewrite README with venv setup, run, test and docs instructions
- Ignore docs/build/ in .gitignore
