Don't presume pip

[rsyring]

• We currently presume pip is available to install uv
• When uv is already present on the system, mise will use uv to create a project virtualenv
  • uv virtualenvs do not install pip
• reqs bootstrap will then try to install uv with pip and throw an error b/c pip isn't available

Related: why are we installing uv if it's already present?

[rsyring]

FYI, you can tell UV to install pip when it creates the virtualenv:

[env]
_.python.venv.path = '{% if env.VIRTUALENVS_DIR %}{{ env.VIRTUALENVS_DIR }}/reach-v2{% else %}.venv{% endif %}'
_.python.venv.create = true
_.python.venv.uv_create_args = ['--seed']