Add exporting functionality. Currently spits out a zip file

[nichochar]

See video for experience.

CleanShot.2024-10-21.at.12.55.38.mp4

Some notes: I did not use the browser API to natively select a directory because:

• this has security limitations and doesn't work well in all browsers, like arc
• won't necessarily work the same when we build a cloud hosted version

Currently, I package up a zip and send it to the Downloads folder. This is a fine MVP pass that we can refine later.

Introduced the archiver package, which allows us to do stream zipping later (even if we don't do it now, it's a better thing to have in place and the library seems very mature).