Native iOS sign-in

iOS authentication now uses the native Firebase flow, with stronger callback, retry, and phone-verification error handling.

The iOS app now completes Firebase authentication through the native plugin instead of relying on the previous fallback path.

What’s new

Added the native Firebase Auth bridge for iOS.
Handled native authentication callbacks and recovery when a request stalls or fails.
Correlated phone-verification failures so the app can report the right error to the right attempt.

Why it matters

Sign-in and phone verification now have a single iOS-specific path with clearer recovery behavior.