fix: build RoadMarking shape in its rotated axes

RoadMarking's local axes are rotated relative to other objects: z is bottom-to-top of the 2D image, not "up". UpdateShapeAndBounds() built its fallback rectangle in the xy plane like other objects, producing a degenerate shape. Use the yz plane with width/height instead, and update GroundTruth to populate dimension.height and pitch.