PyQt5.Qwt isn't pip-installable; it only existed via the apt package
python3-pyqt5.qwt, so pip-installing client/requirements.txt's plain
PyPI PyQt5 always crashed with "No module named 'PyQt5.Qwt'".
Qwt was only used for 3 QwtSlider widgets (Slider_temp_soll,
Slider_pwr_soll, Slider_speed_soll). Swap them for stock QSlider in
brewpi.ui, regenerate brewpi_win.py via pyuic5, and update
brewpi_gui.py's setLowerBound/setUpperBound calls to QSlider's
integer-only setMinimum/setMaximum. The GUI now runs from a plain
`pip install -r client/requirements.txt` venv with no system PyQt5
packages required.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>