Bound Web designer slot controls to their container so nested controls stay resizable

In the Web page designer, a control placed inside a container (for example a Button inside a GroupBox) can end up far larger than the container itself. Once that happens the control cannot be made smaller again from the canvas: the resize handles along its bottom edge are drawn below the bottom of the scrollable designer canvas, so they can never be grabbed, and dragging the top handles never produces a visibly smaller control. The user's only recovery today is typing Row Span / Column Span values in the Inspector's Placement section.

Expected behaviour: a nested control should never be able to span more rows than its container's content area provides, its resize handles should always be reachable, and layouts saved by older versions that already contain oversized nested controls should be normalised on open.