Handle pdf files in chat

This may be more a future option, but it's far more efficient to upload a file and then reference the file rather than send it as filedata. base64-encoded content is treated like raw input. The model must process the file contents as tokens which can get pretty expensive. Also, not very scalable for large files and can even get truncated. I believe it also counts against your context window..

I'd be in favor of looking at how we could use the file upload + thread to enhance this