FIX: install uv through pip

[redeboer]

Since uv v0.2.0, uv is stricter with python discovery. It is now cleaner to run python -m uv where python comes from the virtual environment you are using.

For this, it is required to install uv into the environment instead of having it installed system-wide. This can simply be done with python -m pip install 'uv>=0.2.0.

The new .readthedocs.yml has been tested on ComPWA/compwa.github.io#279.