Use uv's pip interface (uv venv + uv pip) as a fast drop-in replacement for pip, virtualenv, and pip-tools

Documented steps

1. Create a virtual environment: `uv venv` (creates .venv in the current directory; `uv venv path/ -p 3.11` picks location and Python version).
2. Activate it (`source .venv/bin/activate` on Unix, `.venv\Scripts\activate` on Windows) — or skip activation: uv pip commands automatically discover an active VIRTUAL_ENV or a `.venv` in the current/parent directories.
3. Install/manage packages: `uv pip install 'flask>=3'`, `uv pip install -r requirements.txt`, `uv pip uninstall flask`, `uv pip list`, `uv pip freeze`, `uv pip show flask`, `uv pip check`, `uv pip tree`.
4. pip-tools workflow: `uv pip compile pyproject.toml -o requirements.txt` (also accepts requirements.in; supports --extra/--all-extras and --group for PEP 735 groups), then `uv pip sync requirements.txt` to make the environment exactly match the file.
5. Docs: https://docs.astral.sh/uv/pip/ (environments: https://docs.astral.sh/uv/pip/environments/, compile: https://docs.astral.sh/uv/pip/compile/)