Show debugging info in blot

It'd really help for submitting bugs to have a way I can pull these details:

- hash of the script being eval'd (I've had a couple cases where it's unclear if my new script is running b/c it's showing lines I deleted in console.log)
- last run timestamp (for same reason as above)
- current build (ie. how HCB has the git commit hash muted in a footer & detects if it's a dirty build)

Start by tracing how blot evaluates scripts and where its build metadata is available. Determine how to expose the evaluated script hash, last-run timestamp, and current build commit or dirty state. Done means users can retrieve all three details when submitting a bug.

Written by the indexing model from the issue text.