Thumbnail Review

I think it may be inevitable that there must be some user-feedback step in adjusting the frames detected from the thumbnail pass. We can do this in one of three ways:

1. Host a minimal local web server and have a little web page that displays the thumbnail and let's users dynamically select stuff about the frame. This is nice because it's "simple" and doesn't need any other GUI stuff.
2. Native GUI popup window.
3. In-terminal images. Modern terminals (but not all) support rending images. It works fine for me on kitty and would keep this all CLI, but would probably piss off windows users not using Windows Terminal and Mac people not using iTerm2.