[Quassel-IRC] Feature #1897 - Port to QT6

Hi,

as there are quassel-irc fellows around...

Sputnik writes on 02-Apr-2025:

I plan to do this within the next few months. Need to find the time
for it, but I'm slowly gearing up to work on this.

Best thanks and regards,
-Sedat-

Link: https://bugs.quassel-irc.org/issues/1897#change-4659