better user API sort

modules/api/src/main/UserApi.scala

@@ -44,7 +44,10 @@ private[api] final class UserApi(
     case Some(teamId) ⇒ lila.team.MemberRepo.userIdsByTeam(teamId) flatMap UserRepo.byIds
     case None ⇒ $find($query(
       $select.all ++ (engine ?? UserRepo.engineSelect)
-    ) sort UserRepo.sortRatingDesc, makeNb(nb, token))
+    ) sort ((~engine).fold(
+        UserRepo.sortCreatedAtDesc,
+        UserRepo.sortRatingDesc
+      )), makeNb(nb, token))
   }) flatMap { users ⇒
     users.map(u ⇒ makeUrl(R User u.username)).sequenceFu map { urls ⇒
       Json.obj(

modules/user/src/main/UserRepo.scala

@@ -96,6 +96,7 @@ trait UserRepo {
 
   val sortRatingDesc = $sort desc "rating"
   val sortProgressDesc = $sort desc "progress"
+  val sortCreatedAtDesc = $sort desc User.BSONFields.createdAt
 
   def incNbGames(id: ID, rated: Boolean, ai: Boolean, result: Option[Int]) = {
     val incs = List(