feat(render): logical style metrics with a UI scale, so chrome has a consistent physical size

adapters/gtk4/gtk_plot_area.cpp

@@ -303,6 +303,12 @@ void PlotArea::render() noexcept {
   last_render_s_ = started;
   if (frame_) frame_(*plot_, dt);
 
+  // The mapping's factor is the display's scale, so the renderer draws its logical
+  // style metrics at the same ratio the viewport and every forwarded coordinate are
+  // in: a 12 px label is the same physical size on a 1x and a 2x widget. It is the
+  // `::resize` ratio, not `gtk_widget_get_scale_factor()` -- the latter is the
+  // ceiling under fractional scaling and would over-scale the chrome by up to 60%.
+  renderer_->style().ui_scale = mapping_.factor;
   renderer_->begin_frame(static_cast<u32>(viewport.w), static_cast<u32>(viewport.h), viewport);
   renderer_->draw(*plot_);
   renderer_->end_frame();