The code was shown in a native Alert, which has no programmatic
dismiss: after another device authorized the code and polling logged
the user in, the alert stayed open on top of the app.
Replace it with an in-app bottom sheet that closes itself once the
session is authorized. Dismissing only hides the code - polling
continues so login still completes if the code is authorized
afterwards; polling stops when leaving the login screen (parity with
TVLogin). The code can be tapped to copy (expo-clipboard, probed via
requireOptionalNativeModule so builds without the native module just
no-op).
