isLoggedIn Provider

Convenience FutureProvider that reads isLoggedIn from AuthStorageService once. Most of the shell uses authStateProvider directly; this provider is here for places that want a Future<bool> rather than a live AuthState.

1. authStorageProvider exposes AuthStorageService() (re-instantiated per provider build).
2. isLoggedInProvider reads it and forwards AuthStorageService.isLoggedIn().
3. Future resolves once; the provider caches the result until ref.invalidate.

• Stale after logout — code that consumes this must invalidate or prefer authStateProvider for live updates.
• Returns false for the (logged in but tokens cleared) edge case because isLoggedIn flag is what's checked, not the tokens themselves.

• lib/src/features/shared/home/provider/provider.dart:11 // authStorageProvider
• lib/src/features/shared/home/provider/provider.dart:15 // isLoggedInProvider
• lib/src/core/services/auth_storage.dart:81 // isLoggedIn

Duplicates a slice of AuthStateNotifier's responsibility — keep only one source of truth in new code.