Add comment explaining fallback logic in startDrag

Co-authored-by: lavrton <1443320+lavrton@users.noreply.github.com>

src/Node.ts

@@ -2600,6 +2600,8 @@ export abstract class Node<Config extends NodeConfig = NodeConfig> {
       {
         type: 'dragstart',
         target: this,
+        // Use the stored start event if available (from mousedown/touchstart),
+        // otherwise fall back to the provided event (when startDrag is called programmatically)
         evt: (elem.startEvent && elem.startEvent.evt) || (evt && evt.evt),
       },
       bubbleEvent