fix(auth): stop showing error dialog when Google sign-in is cancelled

[demolaf]

Fixes #2422.

Cancelling the Google sign-in Credential Manager sheet showed an "Authentication Error" dialog with the raw GetCredentialCancellationException message ("User cancelled the selector") as the button text, instead of returning silently via AuthState.Cancelled. signInWithGoogle only caught kotlinx.coroutines.CancellationException, not the actual exception Credential Manager throws on dismissal, so it fell through to the generic error path.

• GoogleAuthProvider+FirebaseAuthUI.kt: catches GetCredentialCancellationException explicitly and updates AuthState.Cancelled without rethrowing, so the sign-in flow returns to the picker silently and onSignInCancelled fires.
• ErrorRecoveryDialog.kt: getRecoveryActionText no longer uses the raw exception message as the button label for AuthCancelledException.

Added a test covering the Credential Manager cancellation path, and fixed ErrorRecoveryDialogLogicTest to exercise the real (now-internal) dialog logic functions instead of a stale duplicate that had drifted from the actual code.

[gemini-code-assist]

Code Review

This pull request adds handling for GetCredentialCancellationException when a user dismisses the Credential Manager sheet during Google Sign-In, updating the authentication state to AuthState.Cancelled without throwing an exception. It also changes the visibility of getRecoveryMessage, getRecoveryActionText, and isRecoverable in ErrorRecoveryDialog.kt from private to internal, enabling direct testing and the removal of redundant helper methods in ErrorRecoveryDialogLogicTest.kt. There are no review comments, and I have no feedback to provide.