feat(authentication): update state to use exception object

Refactors `AuthenticationState` to replace the `errorMessage` string with a `HtHttpException` object named `exception`.

This change is necessary to support the new `ht_ui_kit` package, which provides a `toFriendlyMessage` extension on `HtHttpException` for displaying localized error messages. Storing the full exception object in the state allows the UI layer to access it directly and use the extension, ensuring consistent and localized error handling.

Author: fulleni

lib/authentication/bloc/authentication_state.dart

@@ -35,7 +35,7 @@ final class AuthenticationState extends Equatable {
     this.status = AuthenticationStatus.initial,
     this.user,
     this.email,
-    this.errorMessage,
+    this.exception,
   });
 
   /// The current status of the authentication process.
@@ -47,25 +47,25 @@ final class AuthenticationState extends Equatable {
   /// The email address involved in the current authentication flow.
   final String? email;
 
-  /// The error message describing an authentication failure, if any.
-  final String? errorMessage;
+  /// The error describing an authentication failure, if any.
+  final HtHttpException? exception;
 
   @override
-  List<Object?> get props => [status, user, email, errorMessage];
+  List<Object?> get props => [status, user, email, exception];
 
   /// Creates a copy of this [AuthenticationState] with the given fields
   /// replaced with the new values.
   AuthenticationState copyWith({
     AuthenticationStatus? status,
     User? user,
     String? email,
-    String? errorMessage,
+    HtHttpException? exception,
   }) {
     return AuthenticationState(
       status: status ?? this.status,
       user: user ?? this.user,
       email: email ?? this.email,
-      errorMessage: errorMessage ?? this.errorMessage,
+      exception: exception ?? this.exception,
     );
   }
 }