Add "root cause analysis" workflow

[dcramer]

TBD on what and how we expose this, but this is the good version of "what is a bug" that is powering Seer/Autofix in Sentry

My thoughts are either via an ISSUE ID or a filename, same flow as today, expose a clean language for "root cause this error and suggest a solution". We'd want Seer to provide a native diff format as part of it so there's not excess work going into Cursor (and it can leverage all of our context).