[backport core/1.42] fix: App mode - renaming widgets on subgraphs (#10245) (#10469)

## Summary

- Backport of #10245 to `core/1.42`
- Fixes renaming of widgets from subgraph nodes in app builder/app mode

## Conflict resolution

- `src/utils/widgetUtil.test.ts`: Accepted PR's behavior changes
(subgraph nodes resolve without explicit parents), kept target branch's
`_subgraphSlot.label` test, removed now-contradicted "does not resolve
for subgraph node without parents" test

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┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10469-backport-core-1-42-fix-App-mode-renaming-widgets-on-subgraphs-10245-32d6d73d36508150adcafab638b4874e)
by [Unito](https://www.unito.io)

src/components/builder/AppModeWidgetList.vue

@@ -191,7 +191,11 @@ function nodeToNodeData(node: LGraphNode) {
         ]"
       >
         <template #button>
-          <Button variant="textonly" size="icon">
+          <Button
+            variant="textonly"
+            size="icon"
+            data-testid="widget-actions-menu"
+          >
             <i class="icon-[lucide--ellipsis]" />
           </Button>
         </template>