fix(auth): emit AuthResult on sign-in success and fix MFA tooltip auto-open

[demolaf]

Closes #2318 .

All providers called updateAuthState(Idle) after sign-in, so the only AuthState.Success came from Firebase's AuthStateListener which never carries an AuthResult. The result?.let guard in FirebaseAuthScreen then silently blocked onSignInSuccess every time.

Fix: emit AuthState.Success with the real AuthResult via a shared updateAuthStateWithResult() helper. Also fixes MFA tooltip auto-opening when disabled.

[gemini-code-assist]

Code Review

This pull request refactors the authentication state management to provide more detailed feedback upon successful sign-in. Specifically, it introduces updateAuthStateWithResult in FirebaseAuthUI to transition the state to AuthState.Success (including AuthResult and user details) rather than simply returning to Idle. These changes are propagated across Anonymous, Email, and OAuth providers, with corresponding updates to unit tests. The PR also includes UI adjustments to tooltip visibility. Feedback was provided to revert the USE_AUTH_EMULATOR flag in the demo app to false to ensure it remains functional for users without a local emulator setup.