Lobby: include HostUserId in GameStateDto and let client derive host status; update tests

SlipItIn.Server/Services/GameService.cs

@@ -293,6 +293,7 @@ public class GameService : IGameService
             LobbyCode = game.LobbyCode,
             Status = game.Status.ToString(),
             Players = playerInfos,
+            HostUserId = game.HostId,
             CurrentRound = currentRound?.RoundNumber ?? 0,
             RoundTimeRemaining = roundTimeRemaining
         };