Does the new assets system not let ComfyUI work offline anymore?

### 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

ComfyUI works offline as normal, which was working fine a few days ago before the new asset system PR yesterday.

### Actual Behavior

ComfyUI will not load. The web interface will not load. There are errors in the console.

### Steps to Reproduce

New ComfyUI install, run ComfyUI with all internet access disabled.

### Debug Logs

```powershell
Traceback (most recent call last):
File "/home/appuser/.local/lib/python3.13/site-packages/aiohttp/web_protocol.py", line 510, in _handle_request
resp = await request_handler(request)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/appuser/.local/lib/python3.13/site-packages/aiohttp/web_app.py", line 569, in _handle
return await handler(request)
^^^^^^^^^^^^^^^^^^^^^^
File "/home/appuser/.local/lib/python3.13/site-packages/aiohttp/web_middlewares.py", line 117, in impl
return await handler(request)
^^^^^^^^^^^^^^^^^^^^^^
File "/app/ComfyUI/middleware/cache_middleware.py", line 27, in cache_control
response: web.Response = await handler(request)
^^^^^^^^^^^^^^^^^^^^^^
File "/app/ComfyUI/server.py", line 83, in deprecation_warning
response: web.Response = await handler(request)
^^^^^^^^^^^^^^^^^^^^^^
File "/app/ComfyUI/server.py", line 173, in origin_only_middleware
response = await handler(request)
^^^^^^^^^^^^^^^^^^^^^^
File "/app/ComfyUI/server.py", line 689, in get_object_info
seed_assets(["models"])
~~~~~~~~~~~^^^^^^^^^^^^
File "/app/ComfyUI/app/assets/scanner.py", line 78, in seed_assets
with create_session() as sess:
~~~~~~~~~~~~~~^^
File "/app/ComfyUI/app/database/db.py", line 112, in create_session
return Session()
TypeError: 'NoneType' object is not callable
```

### Other

_No response_