refactor(api): simplify anonymous route with ResponseHelper

Updates the `/api/v1/auth/anonymous` route handler to use the new
`ResponseHelper.success` method. This change removes several lines of
boilerplate code related to manually creating metadata and the success
response object, making the handler cleaner and more focused on its
core logic.

Author: fulleni

routes/api/v1/auth/anonymous.dart

@@ -1,11 +1,10 @@
 import 'dart:io';
 
 import 'package:dart_frog/dart_frog.dart';
+import 'package:ht_api/src/helpers/response_helper.dart';
 import 'package:ht_api/src/services/auth_service.dart';
 import 'package:ht_shared/ht_shared.dart';
 
-import '../../../_middleware.dart';
-
 /// Handles POST requests to `/api/v1/auth/anonymous`.
 ///
 /// Creates a new anonymous user and returns the User object along with an
@@ -29,22 +28,11 @@ Future<Response> onRequest(RequestContext context) async {
       token: result.token,
     );
 
-    // Create metadata, including the requestId from the context.
-    final metadata = ResponseMetadata(
-      requestId: context.read<RequestId>().id,
-      timestamp: DateTime.now().toUtc(),
-    );
-
-    // Wrap the payload in the standard SuccessApiResponse
-    final responsePayload = SuccessApiResponse<AuthSuccessResponse>(
+    // Use the helper to create a standardized success response
+    return ResponseHelper.success(
+      context: context,
       data: authPayload,
-      metadata: metadata,
-    );
-
-    // Return 200 OK with the standardized, serialized response
-    return Response.json(
-      // Use the toJson method, providing the toJson factory for the inner type
-      body: responsePayload.toJson((authSuccess) => authSuccess.toJson()),
+      toJsonT: (data) => data.toJson(),
     );
   } on HtHttpException catch (_) {
     // Let the central errorHandler middleware handle known exceptions