Windows Environment and Python installation issue (TypeIs)

Hey!

Just downloaded the windows one-click installer version and after running update.bat and then run.bat I get this error:

```
Traceback (most recent call last):
File "C:\Users\User\Dir\framepack_cu126_torch26\webui\demo_gradio.py", line 8, in
import torch
File "C:\Users\User\Dir\framepack_cu126_torch26\system\python\lib\site-packages\torch\__init__.py", line 75, in
from typing_extensions import TypeIs as _TypeIs
ImportError: cannot import name 'TypeIs' from 'typing_extensions' (C:\Users\User\AppData\Roaming\Python\Python310\site-packages\typing_extensions.py)
Press any key to continue . . .
```

It seems like the environment isn't being set correctly / it uses the system python, not its own internal one.

running 'where python' in the .bat reveals two python installations:
```
C:\Users\User\Dir\framepack_cu126_torch26\system\python\python.exe
C:\Program Files\Python310\python.exe
```

The current script also doesn't seem to support Powershell and CMD at the same time. But that'd be just a small quality of life change i guess.

Start with update.bat and run.bat, then inspect the Python import at webui/demo_gradio.py:8 and the reported typing_extensions path. Reproduce the one-click installation on Windows and verify that the bundled Python is used and that the scripts work from both CMD and PowerShell.

Written by the indexing model from the issue text.