StretchHeaderView: Set default section size

As of Qt 6.6.1, style changes are resetting the column sizes. To prevent this, we set a default section size.

Fixes #1328

src/widgets/stretchheaderview.cpp

@@ -46,6 +46,7 @@ StretchHeaderView::StretchHeaderView(const Qt::Orientation orientation, QWidget
   QObject::connect(this, &StretchHeaderView::sectionResized, this, &StretchHeaderView::SectionResized);
   setMinimumSectionSize(kMinimumColumnWidth);
   setTextElideMode(Qt::ElideRight);
+  setDefaultSectionSize(100);
 
 }