add thumbnail for 3d generation (#8129)

## Summary

add thrumbnail for 3d genations, feature requested by @PabloWiedemann 

## Screenshots


https://github.com/user-attachments/assets/4fb9b88b-dd7b-4a69-a70c-e850472d3498

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8129-add-thumbnail-for-3d-generation-2eb6d73d365081f2a30bc698a4fde6e0)
by [Unito](https://www.unito.io)

src/composables/useLoad3d.ts

@@ -511,6 +511,22 @@ export const useLoad3d = (nodeOrRef: MaybeRef<LGraphNode | null>) => {
       hasSkeleton.value = load3d?.hasSkeleton() ?? false
       // Reset skeleton visibility when loading new model
       modelConfig.value.showSkeleton = false
+
+      if (load3d) {
+        const node = nodeRef.value
+
+        const modelWidget = node?.widgets?.find(
+          (w) => w.name === 'model_file' || w.name === 'image'
+        )
+        const value = modelWidget?.value
+        if (typeof value === 'string') {
+          void Load3dUtils.generateThumbnailIfNeeded(
+            load3d,
+            value,
+            isPreview.value ? 'output' : 'input'
+          )
+        }
+      }
     },
     skeletonVisibilityChange: (value: boolean) => {
       modelConfig.value.showSkeleton = value