Change default attribution on Spoke scenes

Currently, scenes uploaded in Spoke have the default attribution JC. Often people don't change this when they upload their test scenes, which makes it hard to know which scenes were actually created by JC (see screenshot). It would be nice if the default was perhaps blank or "Anonymous."

Start by locating the Spoke scene upload flow and the code that supplies the default attribution. Confirm how attribution is stored on uploaded scenes, then change the default to the agreed blank or "Anonymous" value and verify that newly uploaded test scenes use it.

Written by the indexing model from the issue text.