handleResizeStart method
Implementation
void handleResizeStart(String itemId, Offset startPosition, Size currentSize) {
resizingItemId.value = itemId;
originalItemSize.value = currentSize;
resizeStartPosition.value = startPosition;
// Prevent dragging while resizing
draggingItemId.value = null;
originalItemPosition.value = null;
itemStartPosition.value = null;
}