[DevTask] Configure Content-Disposition on downloaded files

Currently we rely on the security convention that browsers will not attempt to run binary files, and change their MIME type to binary.

Recommendation is to actually instruct the browser to download files by setting`Content-Disposition` properly.

https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Disposition#syntax

```
Content-Disposition: attachment; filename="download-me.html"
```

https://github.com/comfyanonymous/ComfyUI/blob/312d511630db4907c3bed04dee297b28f61941a8/server.py#L485-L488