Signing fix

Fixed

• Signing in brings Studio back to the front by itself, and the browser tab closes behind it. No more finishing in the browser and wondering which window to go find.
• A sign-in that fails now says why, right under the button — an expired code, a timeout, a backend that didn't answer. It used to fail in total silence, which looked like the button doing nothing.
• Fixed a race where finishing sign-in too quickly — already logged in to Heal in your browser, so the round trip is instant — left the app waiting the full two minutes before giving up on a code it had already received.