Make Viewer mode consider the presence of the task bar

[flipflop]

Arch Linux, KDE Plasma 6.2.5, Qt 6.8.1, Wayland
(I'm not sure if this also applies to Windows)

Currently if I set "Fit image to desktop" in Viewer mode, it does not take the task bar into consideration. This means that large images are resized to the screen height, and the task bar covers the bottom part of the image. My suggestion is that the images should be resized to screen height minus the height of the task bar, so that the whole image is visible