ComfyUI persistently loads old workflow despite clean install and data deletion

### 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

When launching ComfyUI (whether it's an installer version or portable), I expect it to start with a blank, default workflow. Additionally, if I have a workflow open, I expect to be able to close it and return to a blank state, which is currently not possible with the persistently loaded old workflow.

### Actual Behavior

I'm experiencing a very persistent and frustrating issue with ComfyUI on Windows 11. Regardless of whether I use the installer or the portable version, ComfyUI always launches with a specific older workflow automatically loaded. **This workflow cannot be closed or cleared from the interface; there's no option to return to a blank canvas.** This makes it impossible to start with a clean state or switch to a new, empty workflow.

Ubale to rid off:

### Steps to Reproduce

* **Complete uninstallation:** For the installer version, I used the standard uninstallation process.
* **Manual data deletion:** I manually deleted all related data from `AppData\Local` (including `C:\Users\\AppData\Local\Programs\@comfyorgcomfyui-electron` which was the old installation path) and `AppData\Roaming\ComfyUI`.
* **Clearing temporary files:** I've cleared the contents of the `%TEMP%` folder.
* **Browser cache/data:** I've cleared the cache and data of my web browser (Chrome/Edge/Firefox).
* **Clean Portable Install:** I downloaded the latest portable version of ComfyUI and extracted it to a new location, but it still loads the old workflow.
* **Custom Node Disablement:** I have launched ComfyUI with the `--disable-all-custom-nodes` command line argument, and the issue persists even without any custom nodes active.

### Debug Logs

```powershell
Checkpoint files will always be loaded safely.
Total VRAM 16376 MB, total RAM 64667 MB
pytorch version: 2.7.1+cu128
Set vram state to: NORMAL_VRAM
Device: cuda:0 NVIDIA GeForce RTX 4080 : cudaMallocAsync
Using pytorch attention
Python version: 3.12.10 (tags/v3.12.10:0cc8128, Apr 8 2025, 12:21:36) [MSC v.1943 64 bit (AMD64)]
ComfyUI version: 0.3.43
ComfyUI frontend version: 1.23.4
[Prompt Server] web root: D:\Temp\ComfyUI_windows_portable\python_embeded\Lib\site-packages\comfyui_frontend_package\static

Import times for custom nodes:
0.0 seconds: D:\Temp\ComfyUI_windows_portable\ComfyUI\custom_nodes\websocket_image_save.py

Context impl SQLiteImpl.
Will assume non-transactional DDL.
No target revision found.
Starting server

To see the GUI go to: http://127.0.0.1:8188
```

### Other

_No response_