refactor(api): relocate RequestId to lib for proper access

Moves the `RequestId` class from `routes/_middleware.dart` to a new,
more appropriate location at `lib/src/models/request_id.dart`. This
resolves an architectural issue where a helper class in `lib/` could not
access a model defined in `routes/`.

All references to `RequestId` in the root middleware and the new
`ResponseHelper` have been updated to use the new, correct import path.
This change improves code structure and enables further refactoring.

Author: fulleni

lib/src/helpers/response_helper.dart

@@ -1,10 +1,9 @@
 import 'dart:io';
 
 import 'package:dart_frog/dart_frog.dart';
+import 'package:ht_api/src/models/request_id.dart';
 import 'package:ht_shared/ht_shared.dart';
 
-import '../../routes/_middleware.dart';
-
 /// A utility class to simplify the creation of standardized API responses.
 abstract final class ResponseHelper {
   /// Creates a standardized success JSON response.

lib/src/models/request_id.dart

@@ -0,0 +1,39 @@
+/// {@template request_id}
+/// A wrapper class holding a unique identifier (UUID v4) generated for each
+/// incoming HTTP request.
+///
+/// **Purpose:**
+/// The primary role of this ID is **traceability for logging and debugging**.
+/// It allows developers to follow the entire lifecycle of a *single request*
+/// through various middleware, route handlers, repository calls, and potential
+/// external service interactions by searching logs for this specific ID.
+/// If an error occurs during a request, this ID provides a way to isolate all
+/// related log entries for that specific transaction, simplifying debugging.
+///
+/// **Scope:**
+/// - The ID is **transient** for the request itself; it exists only during the
+///   request-response cycle.
+/// - It is **not persisted** in the main application database alongside models
+///   like Headlines or Categories.
+/// - Its value lies in being included in **persistent logs**.
+///
+/// **Distinction from other IDs:**
+/// - **User ID:** Identifies the authenticated user making the request. Often
+///   logged alongside the `request_id` for user-specific debugging.
+/// - **Session ID:** Tracks a user's session across multiple requests.
+/// - **Correlation ID:** Often generated by the *client* and passed in headers
+///   to link related requests initiated by the client for a larger workflow.
+///
+/// **Implementation:**
+/// This class ensures type safety when providing and reading the request ID
+/// from the Dart Frog context using `context.provide<RequestId>` and
+/// `context.read<RequestId>()`. This prevents potential ambiguity if other raw
+/// strings were provided into the context.
+/// {@endtemplate}
+class RequestId {
+  /// {@macro request_id}
+  const RequestId(this.id);
+
+  /// The unique identifier string (UUID v4).
+  final String id;
+}

routes/_middleware.dart

@@ -1,5 +1,6 @@
 import 'package:dart_frog/dart_frog.dart';
 import 'package:ht_api/src/config/app_dependencies.dart';
+import 'package:ht_api/src/models/request_id.dart';
 import 'package:ht_api/src/middlewares/error_handler.dart';
 import 'package:ht_api/src/rbac/permission_service.dart';
 import 'package:ht_api/src/registry/model_registry.dart';
@@ -15,48 +16,6 @@ import 'package:ht_shared/ht_shared.dart';
 import 'package:logging/logging.dart';
 import 'package:uuid/uuid.dart';
 
-// --- Request ID Wrapper ---
-
-/// {@template request_id}
-/// A wrapper class holding a unique identifier (UUID v4) generated for each
-/// incoming HTTP request.
-///
-/// **Purpose:**
-/// The primary role of this ID is **traceability for logging and debugging**.
-/// It allows developers to follow the entire lifecycle of a *single request*
-/// through various middleware, route handlers, repository calls, and potential
-/// external service interactions by searching logs for this specific ID.
-/// If an error occurs during a request, this ID provides a way to isolate all
-/// related log entries for that specific transaction, simplifying debugging.
-///
-/// **Scope:**
-/// - The ID is **transient** for the request itself; it exists only during the
-///   request-response cycle.
-/// - It is **not persisted** in the main application database alongside models
-///   like Headlines or Categories.
-/// - Its value lies in being included in **persistent logs**.
-///
-/// **Distinction from other IDs:**
-/// - **User ID:** Identifies the authenticated user making the request. Often
-///   logged alongside the `request_id` for user-specific debugging.
-/// - **Session ID:** Tracks a user's session across multiple requests.
-/// - **Correlation ID:** Often generated by the *client* and passed in headers
-///   to link related requests initiated by the client for a larger workflow.
-///
-/// **Implementation:**
-/// This class ensures type safety when providing and reading the request ID
-/// from the Dart Frog context using `context.provide<RequestId>` and
-/// `context.read<RequestId>()`. This prevents potential ambiguity if other raw
-/// strings were provided into the context.
-/// {@endtemplate}
-class RequestId {
-  /// {@macro request_id}
-  const RequestId(this.id);
-
-  /// The unique identifier string (UUID v4).
-  final String id;
-}
-
 // --- Middleware Definition ---
 final _log = Logger('RootMiddleware');