Extend the response API to handle multipart/form-data as a way to return pictures of the screen to the trafficlight server

For instance, we should return screenshots of avatars, of embedded videos, of images displayed in the timeline for comparison and longer-term storage.

Start by locating the response API entry point in the trafficlight server and inspect how responses are currently represented. Confirm the multipart/form-data shape and how screenshots should be returned for avatars, embedded videos, and timeline images; done means the API can return those pictures for comparison and longer-term storage.

Written by the indexing model from the issue text.