Add a hierarchy view for window controls

Add a Structure-style view in Objo Studio showing the parent/child hierarchy of controls on the current window. This would give users a visual way to understand how controls are organised, because the Inspector currently lists controls alphabetically rather than by containment.

The view should make it easy to inspect nested controls and select a control from the hierarchy while working in the visual designer. It could be docked as another tab near the Inspector or available as a floating window, depending on user preference.