text: Title: [Feature Request] App Window: standardize on pywebview[qt]
  Body: ### Description
  
  This request involves the window icon for local app mode.
  
  According to the [pyproject.toml](https://github.com/rio-labs/rio/blob/main/pyproject.toml), pywebview 4.2 is installed on Windows with cefpython and current (5.3.2) is installed on Linux with QT. However, of these two only the QT backend supports runtime icons, per [the pywebview documentation](https://pywebview.flowrl.com/examples/icon.html).
  
  ### Suggested Solution
  
  Standardizing on the QT backend would allow for identical support on Windows, Mac, and Linux, with app icon support. QTPY is arguably better supported in general, as cefpython3 has not been updated in years.
  
  ### Alternatives
  
  N/A - see [NiceGUI pull 634](https://github.com/zauberzeug/nicegui/pull/634)
  
  ### Additional Context
  
  The [window] subinstall is broken on Ubuntu 22.04, as the unsupported pywebview 4.2 is installed in addition to current. If this feature request is not accepted, please update pyproject.toml line 76 to read:
  
  `    "pywebview~=4.2" ; sys_platform == 'win32'",`
  
  Separately, cefpython3 is [available for Mac on Python 3.10]( https://pypi.org/project/cefpython3-v66.1-for-python-3.10.2-unofficial/).
  
  ### Related Issues/Pull Requests
  
  _No response_