createWhiteboard

Create a whiteboard: an infinite freeform canvas. A whiteboard is a hidden document (it won't appear in listDocuments) that hosts a single freeform canvas, and opens in the immersive whiteboard editor in the app. Returns documentId + diagramId. Author shapes afterwards with addWhiteboardElements (high-level specs) or updateWhiteboardScene. For anything beyond a blank board, call getWhiteboardGuide first to plan the layout (stencils vs architecture icons vs code/BPMN diagrams vs plain shapes), and render with getWhiteboardImage to verify as you go.