Keep file dialogs within the app window

[yashranaway]

<<<< AI wording below >>>>

Problem

Under the GTK platform theme, Qt Quick Dialogs uses a native GTK file chooser. On a 2x Wayland display, that chooser can restore a 1231x903 GTK geometry and open beyond the 1280x832 logical work area.

Reported in omacom/omarchy#9046.

Fix

Force Omawrite Open and Save dialogs to use Qt Quick Dialogs built-in implementation. Its Material dialog has a 600x400 logical default and stays inside the application window instead of restoring GTK window geometry.

Add object names and a unit check that both dialogs set DontUseNativeDialog.

Verification

• git diff --check
• Compared the dialog behavior with the Qt 6.11.2 FileDialog documentation and Material implementation
• Added usesQuickFileDialogs coverage
• The test suite was not run because this environment lacks qmake and Qt development packages
• Live verification on the reported 2x display is still needed

[yuzuwoeser]

I reproduced this outside Omawrite with a standalone GTK 3 file chooser. GTK converts an already-computed CSS pixel font size by resolution / 72 a second time. That produces the 1203×902 default; removing the leftover conversion gives 880×660, and Omawrite's Qt+GTK path drops from 1231×950 to 908×707.

DontUseNativeDialog bypasses the faulty GTK path by replacing the native picker, so it should not be merged as the fix for this issue. A focused GTK fix is prepared and locally verified against GTK issue #4891. Please close this PR; I’ll link the upstream MR after it is submitted.

[yuzuwoeser]

The upstream GTK fix is now available as GNOME/gtk!10311, with its full CI pipeline passing. The recommendation to close this draft in favor of addressing the GTK root cause is unchanged.