feat(API): optional display name on users

features/get_current_user.feature

@@ -9,9 +9,10 @@ Feature: A logged-in user fetches their own public profile without triggering th
     without being throttled like a login attempt
 
   Background:
-    Given the existing PublicUser struct and newPublicUser(u user.User) converter in
-      api/handlers/auth/verificationHandler.go, exactly the JSON shape POST /v1/auth/verify already
-      returns: id, username, email, is_verified, created_at, updated_at
+    Given the public user struct and its converter, shared by the auth and user handlers from a
+      package under api/pkg (features/user_display_name.feature), exactly the JSON shape
+      POST /v1/auth/verify returns: id, username, email, is_verified, created_at, updated_at and
+      display_name
     And this slice adds GET /v1/auth/me, handled by a new MeHandler (api/handlers/auth/meHandler.go)
       built with NewMeHandler(container.GetUserUseCase), the same GetUserUseCase every other
       protected handler already gets from api/dependecyInjection.go; no new use case or domain