PySide6 consumer packaging

Moved: Python consumer docs live in packaging-python.md (shipped early on 2.64).

Published: packaging-python on GitHub Pages

PySide6-only placeholder from roadmap 2.71; PyQt6 is also supported via QWINUI3_QT_BINDING=pyqt6.

Example: examples/python-gallery/ — full Gallery from Python.

Verification: python scripts/verify_python.py --smoke