fix(auth): report Google/Facebook/OAuth/Anonymous sign-in failures via onSignInFailure

[demolaf]

FirebaseAuthScreen's onSignInFailure callback was only ever invoked from EmailAuthScreen and PhoneAuthScreen's own effects. Google, Facebook, OAuth (Apple/Github/Microsoft/Yahoo/Twitter/generic), and Anonymous sign-in failures only updated the shared AuthState.Error - which the top-level dialog controller shows - but never reached onSignInFailure, so a consuming app's own error logging/analytics wired through that callback silently never fired for those providers.

Threads an onSignInFailure callback into all four remember*SignInHandler functions, calling it alongside each existing updateAuthState(AuthState.Error(...)) so each provider reports its own failure exactly once, at the source - symmetric with how Email/Phone already report theirs.

• GoogleAuthProvider+FirebaseAuthUI.kt, FacebookAuthProvider+FirebaseAuthUI.kt, OAuthProvider+FirebaseAuthUI.kt, AnonymousAuthProvider+FirebaseAuthUI.kt: added an onSignInFailure parameter to each remember*Handler, called in their catch blocks.
• FirebaseAuthScreen.kt: threads onSignInFailure through rememberOnProviderSelected and its two call sites - the main flow passes the real callback; the reauth sheet keeps its existing no-op default, matching how it already no-ops Email/Phone's onError there.

Added direct tests forcing a failure (testCredentialManagerProvider for Google, a failing signInAnonymously() task for Anonymous) confirming onSignInFailure fires immediately without navigating anywhere - verified both are load-bearing by temporarily reverting the fix and confirming they fail.

[gemini-code-assist]

Code Review

This pull request introduces an onSignInFailure callback to various authentication provider handlers (Anonymous, Facebook, Google, and OAuth) and propagates it through the UI and screens to report sign-in failures immediately. While the implementation and accompanying unit tests are solid, there are critical issues regarding Compose state management. Specifically, several remember and DisposableEffect blocks capture the new callback and other dependencies (like context and activity) without including them in their keys. This can lead to stale state captures, memory leaks (particularly with Activity references), and potential crashes. Updating these blocks to include all captured dependencies as keys is highly recommended.