VerificationCodeInputField: iPad Return key clears/hides OTP fields #1407

Environment:

• Swift, iPadOS version: all, FirebaseUI version: do not know exactly (Podfile.lock), Xcode: found it while testing

Steps:

1. Present view using VerificationCodeInputField (e.g. PhoneReauthView)
2. Focus OTP field on iPad with hardware keyboard
3. Press Return repeatedly

Observed: fields disappear one-by-one, unrecoverable without back+Verify
Expected: Return resigns/dismisses or no-ops, fields stay visible

Relevant: FirebaseSwiftUI/FirebaseAuthUIComponents/Sources/Components/VerificationCodeInputField.swift - BackspaceAwareTextField.Coordinator has no textFieldShouldReturn, shouldChangeCharactersIn only blocks non-digits but Return path can hit handleBackspace/clear.