QT6 apps

Hi!

The steps for Qt thus far using qt-styleplugins and qt5ct seem to work for qt5 only. Is it true that so far, QT6 applications are not themed by this project at all?

For QT6 I have found the following to work:

https://aur.archlinux.org/packages/qt6gtk2 -> https://www.opencode.net/trialuser/qt6gtk2

which adds a `qt6gtk2` entry to the `Styles` dropdown in `qt6ct`.

Also I have installed https://www.dafont.com/w95fa.font which is a scaled version of MS Sans Serif and when configured @ font size `9.5` in xfce appearance *and* if this file is created

```

W95FA

false
none
lcdnone
false
true
hintfull

```

it will look crisp and un-antialized everywhere. It's nice because it scales, while MS Serif does not. I've used this font successfully in man applications now.

However, when you use QT6 and also scale them using e.g. `QT_SCALE_FACTOR=something` in `/etc/environment` because qt apps don't respect XFCE's apperance `Window Scaling` setting, then W95FA will become blurry again, while MS Serif won't and neither will the DOS VGA fonts because they're all bitmap-based.

I have also found `QT_QPA_PLATFORMTHEME=qt5ct` to be fine as a global var, it doesn't seem to affect QT6 apps negatively.

With all that said, qt6gtk2 isn't perfect. Some buttons don't show the selection state and icons are often not centered. Here's qBittorrent for example:

The issue names no project files or tests; start by reading the existing Qt and qt5ct guidance, then compare it with qt6ct and qt6gtk2. Confirm whether Qt6 theming is in scope, investigate the reported button, icon, and scaling behavior, and define the supported result before implementation.

Written by the indexing model from the issue text.