fix: undo breaking Vue node image preview reactivity (#8839)

## Summary
restoreOutputs was assigning the same object reference to both
app.nodeOutputs and the Pinia reactive ref. This caused subsequent
writes via setOutputsByLocatorId to mutate the reactive proxy's target
through the raw reference before the proxy write, making Vue detect no
change and skip reactivity updates permanently.

Shallow-copy the outputs when assigning to the reactive ref so the proxy
target remains a separate object from app.nodeOutputs.

## Screenshots
before


https://github.com/user-attachments/assets/98f2b17c-87b9-41e7-9caa-238e36c3c032


after


https://github.com/user-attachments/assets/cb6e1d25-bd2e-41ed-a536-7b8250f858ec

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8839-fix-undo-breaking-Vue-node-image-preview-reactivity-3056d73d365081d2a1c7d4d9553f30e0)
by [Unito](https://www.unito.io)

src/stores/imagePreviewStore.ts

@@ -365,7 +365,7 @@ export const useNodeOutputStore = defineStore('nodeOutput', () => {
     outputs: Record<string, ExecutedWsMessage['output']>
   ) {
     app.nodeOutputs = outputs
-    nodeOutputs.value = outputs
+    nodeOutputs.value = { ...outputs }
   }
 
   function updateNodeImages(node: LGraphNode) {