Fix dark-theme backgrounds across device, HMS, and AMS UI on macOS

Give previously-bare panels a keyed background so the existing dark-UI walk
can theme them. Runtime-created widgets (HMS items, device firmware/nozzle
panels) route their whole subtree through one UpdateDarkUIWin(this) call
instead of per-widget darkModeColorFor, which also themes their child text
and follows live light/dark switches. Extruder-card chips re-apply their
colours from Sidebar::sys_color_changed so a live switch updates them too.

src/slic3r/GUI/UpgradePanel.cpp

@@ -1796,6 +1796,8 @@ bool UpgradePanel::Show(bool show)
                    const wxString &name /*= wxEmptyString*/)
     : wxPanel(parent,id,pos,size,style)
 {
+     SetBackgroundColour(*wxWHITE);
+
      upgrade_green_icon = ScalableBitmap(this, "monitor_upgrade_online", 5);
 
      auto ams_sizer = new wxFlexGridSizer(0, 2, 0, 0);
@@ -1879,6 +1881,7 @@ bool UpgradePanel::Show(bool show)
      const wxString& name /*= wxEmptyString*/)
      : wxPanel(parent, id, pos, size, style)
  {
+     SetBackgroundColour(*wxWHITE);
 
      upgrade_green_icon = ScalableBitmap(this, "monitor_upgrade_online", 5);