uic from Qt 6.12.0 crashes (0xC0000005) on any non-empty <connections>
block in .ui files. Move the cancel_button -> reject connection from
configuration_edit_dialog.ui into configurationEditDialog.cpp, matching
how the other buttons are already connected there.
Also document the glslang (glslangValidator) requirement for Windows
builds; CMake requires it via find_program(... REQUIRED).
