Install custom node extensions from the new extension manager in Windows Desktop 0.6.0 doesn't download the associated models

### Custom Node Testing

- [ ] I have tried disabling custom nodes and the issue persists (see [how to disable custom nodes](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled) if you need help)

### Expected Behavior

When I install ComfyUI Impact Pack and ComfyUI Impact Subpack, not only should the custom nodes install, but the associated models for those nodes should also install (like it did before the old Model manager was removed).

### Actual Behavior

When I install ComfyUI Impact Pack and ComfyUI Impact Subpack, not only should the custom nodes install, but the associated models for those nodes should also install (like it did before the old Model manager was removed). The specific example is the UltralyticsDetectorProvider node. It used to come with the yolov face detection model that was installed to your models/ultralytics folder but now when you install, the models are not downloaded and the models folder is not created.

### Steps to Reproduce

Install ComfyUI Impact Subpack, restart, add the custom node to a workflow and notice that the model is "undefined" rather than showing you the model its using.

### Debug Logs

```powershell
No debug logs, the install just doesn't behave the way it used to.
```

### Other

_No response_

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*This issue is transferred from: https://github.com/comfyanonymous/ComfyUI/issues/11297*

Original issue was created by @bmmathe at 2025-12-12T19:55:50.000Z

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-7455-Install-custom-node-extensions-from-the-new-extension-manager-in-Windows-Desktop-0-6-0-2c86d73d3650815bbc9df801cc802ee6) by [Unito](https://www.unito.io)