fix: add env to isolation python env so user doesn't leak in

[kratsg]

Meant to prevent issues like

[W 2026-03-03 23:03:58.586 ServerApp] ServerApp.token config is deprecated in 2.0. Use IdentityProvider.token.
[W 2026-03-03 23:03:58.590 ServerApp] ServerApp.allow_password_change config is deprecated in 2.0. Use PasswordIdentityProvider.allow_password_change.
[W 2026-03-03 23:03:58.783 ServerApp] dask_labextension | error adding extension (enabled: True): The module 'dask_labextension' could not be found (cannot import name 'HLGExpr' from 'dask._expr' (/home/kratsg/.local/lib/python3.12/site-packages/dask/_expr.py)). Are you sure the extension is installed?
    Traceback (most recent call last):
      File "/app/.pixi/envs/ml/lib/python3.12/site-packages/jupyter_server/extension/manager.py", line 365, in add_extension
        extpkg = ExtensionPackage(name=extension_name, enabled=enabled)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/app/.pixi/envs/ml/lib/python3.12/site-packages/jupyter_server/extension/manager.py", line 219, in __init__
        self._load_metadata()
      File "/app/.pixi/envs/ml/lib/python3.12/site-packages/jupyter_server/extension/manager.py", line 234, in _load_metadata
        raise ExtensionModuleNotFound(msg) from None
    jupyter_server.extension.utils.ExtensionModuleNotFound: The module 'dask_labextension' could not be found (cannot import name 'HLGExpr' from 'dask._expr' (/home/kratsg/.local/lib/python3.12/site-packages/dask/_expr.py)). Are you sure the extension is installed?