[iOS] Pairing with QR code ignores user input name

If you attempt to first-time log in to user xyz on iOS and scan a QR code for user abc, you will pair with abc.

Expected: a warning should pop up saying that the QR code user and the input username are mismatched to prevent accidental pairing.

Workaround: make sure you are always aware of which account is logged in on your terminal at all times.

Reproduce the first-time iOS login flow using a typed username that differs from the user represented by the scanned QR code. Trace the pairing entry point and make completion show a mismatch warning instead of pairing with the QR-code user.

Written by the indexing model from the issue text.