CivitAI Model Downloader node fails due to missing 'filename' argument and unresolved save_dir path

### 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

This issue originally occurred in the community node "ComfyUI Model Downloader" (installed via ComfyUI-Manager, ID: 496).
However, since the repository is currently unavailable (404), I am reporting it here as the issue may be related to core components such as BaseModelDownloader and folder_paths.

Environment:
- Platform: RunPod (Docker-based remote environment)
- OS: Ubuntu (RunPod Slim Template)
- ComfyUI Version: latest (installed via ComfyUI-Manager)
- Python: 3.10
- Node installed via ComfyUI-Manager (ID: 496 - ComfyUI Model Downloader)

### Actual Behavior

When executing the "CivitAI Download" node, the workflow immediately fails with the following error:

CivitAI Downloader
BaseModelDownloader.prepare_download_path() missing 1 required positional argument: 'filename'

In the console log, the following warning also appears:
Warning: Could not resolve path for type 'checkpoints' via folder_paths. Falling back to models_dir.

The node does not start any download process.
The error happens even though the save_dir (e.g., "checkpoints") folder exists at /workspace/runpod-slim/ComfyUI/models/checkpoints.

### Steps to Reproduce

1. Launch ComfyUI on RunPod (Docker-based environment, Ubuntu Slim template)
2. Install "ComfyUI Model Downloader" node via ComfyUI-Manager (Node ID: 496)
3. Create a new workflow and place one "CivitAI Download" node
4. Set the following inputs:
- model_id: 404154
- token_id:
- save_dir: checkpoints
5. Set the node as the last node in the workflow
6. Click the Run button

Result:
The workflow immediately fails with the error:
BaseModelDownloader.prepare_download_path() missing 1 required positional argument: 'filename'

### Debug Logs

```powershell
## Logs

2025-11-04T20:00:15.089261 - Warning: Could not resolve path for type 'checkpoints' via folder_paths. Falling back to models_dir.
2025-11-04T20:00:15.089659 - Warning: Could not resolve path for type 'loras' via folder_paths. Falling back to models_dir.
2025-11-04T20:00:15.089923 - Warning: Could not resolve path for type 'unet' via folder_paths. Falling back to models_dir.

During workflow execution:

CivitAI Downloader
BaseModelDownloader.prepare_download_path() missing 1 required positional argument: 'filename'
```

### Other

_No response_

Start by reproducing the CivitAI Download workflow with model_id 404154 and save_dir set to checkpoints, then inspect BaseModelDownloader.prepare_download_path and the folder_paths resolution mentioned in the logs. The custom node repository is unavailable, so confirm whether the failure is in ComfyUI core. Done means the workflow starts without the missing filename error or unresolved save_dir warning.

Written by the indexing model from the issue text.