Designer ContainerControl inspector missing appearance properties

In the visual designer, selecting a ContainerControl did not expose the runtime BackgroundColour and ClipContents properties in the Inspector. Users could set those properties in code, but could not configure them visually. The designer also failed to expose ScrollBox.BackgroundColour, even though ScrollBox supports that runtime property.

Expected behaviour: ContainerControl shows BackgroundColour and ClipContents in the Inspector, and ScrollBox shows BackgroundColour. Values persist in layout XML, appear in the designer preview, and generate runtime constructor assignments.

Fixed in 02355454.