Opinion: Proper .venv and python project management with uv

[lindestad]

uv is faster, simpler, and more reliable for setting up the project. A pyproject.toml gives us one clear place for Python dependencies and project config. The current setup is too easy to break or let drift between machines. We already hit missing package issues (#24) that a better setup would have avoided. Moving to uv and pyproject.toml would make onboarding easier, installs more repeatable, and the project easier to maintain.