Add support for clipboard input

[ErikBjare]

Would be great to support both text and image contents in clipboard. Would make it a lot easier to ingest information through the clipboard (since we don't support multi-line strings, you currently have to paste contents to a file, or a path to the screenshot).

Suggested by /u/Either-Nobody-3962

[0xbrayo]

Seems simple enough, not sure how to handle image content though, do you just push the base64 string as input. I guess it still can interpret that?

[ErikBjare]

We'd dump the image contents to a tmp file and attach it to the message like any other vision message.

[ErikBjare]

With #244 we now support pasting multiline strings thanks to prompt-toolkit, so the priority on this is now less.

[0xbrayo]

Cool. I guess only the use case now is the screenshot input.