Fix node persistence not flushing after drag ends

The isDraggingRef skip in useGraphPersistence was never re-evaluated
after drag ended because refs don't trigger re-renders. Force a nodes
identity change in onNodeDragStop so the persistence effect re-runs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bchapuis

apps/app/src/components/workflow/use-graph-operations.ts

@@ -760,7 +760,8 @@ export function useGraphOperations({
     }, []),
     onNodeDragStop: useCallback(() => {
       isDraggingRef.current = false;
-    }, []),
+      setNodes((nodes) => [...nodes]);
+    }, [setNodes]),
     isDraggingRef,
     isValidConnection,
     handleAddNode,