fix(client): The Sync flow should not notify the browser of login after the signup confirmation poll completes.

The browser polls in the background for the status of the sign up completion itself, the client does not need to notify it of completion.

In addition, the /confirm screen should not transition to the /signup_complete screen, this causes a jerky UI.

fixes #1881
In trying to resolve this I found what the real regression is: we don't notify the browser of the user's login after we do the signup but have not yet verified. The goal of the original flow was that the user could close the original tab that tells you to check your email (or open the verification link in that tab), and sync would still start. I missed this in review of your refactor @shane-tomlinson, or possibly steered you in a direction that introduced the regression.

The tests help catch this, so there's a positive.