Unable to update ComfyUI via manager

### Custom Node Testing

- [x] 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

Trying to update ComfyUI Portable (Win 11) via the manager and I get this error :

```
[ComfyUI-Manager] Failed to checkout 'master' branch.
repo_path=D:\comfyui\ComfyUI
Available branches:
ComfyUI update failed
```

In the startup log I can see this line :
```

[ComfyUI-Manager] network_mode: public
### ComfyUI Revision: 150 [265adad8] *DETACHED | Released on '2025-11-04'
```

When I run git branch -al in the comfyUI directory it shows :

`* (HEAD detached at v0.3.68)`

Not sure how I managed to 'detach' from the main branch. I just downloaded the portable version and have been using that ever since.

Is there a safe way to update ComfyUI core code without messing up any other nodes/extension that I have installed like sageattention, reactor, etc.

### Actual Behavior

ComfyUI updated to latest via Manager.

### Steps to Reproduce

Goto ComyUI Manager > Click Update ComfyUI

### Debug Logs

```powershell
[ComfyUI-Manager] network_mode: public
### ComfyUI Revision: 150 [265adad8] *DETACHED | Released on '2025-11-04'
```

### Other

_No response_