Improve websim git export script

- Automate aggregating views of the version history by recursively
  clicking earliest version, reopening the versions list,
  and waiting for it to load.
- Prompt user to pick elements to build query selectors from,
  instead of hard-coding fragile selectors.
  (I've mostly re-used my code from the os-gui.js kitchen sink here,
  but I've converted it to use vanilla JS instead of jQuery, and to use
  a promise instead of callback.)
- Add output dialog where you can copy JSON,
  or an LLM prompt for better commit summaries.