Add turn tracking and enforce turn order

Introduce CurrentTurn to Game (default 1) and expose it via GameInformationDto. Update GameManager to include CurrentTurn in the GameInformation payload, validate that a player can only Drop when it is their turn, and toggle CurrentTurn between 1 and 2 after a successful move. Also use a safe fallback (0) when game is null.

API/Services/GameManager/GameManager.cs

@@ -43,7 +43,8 @@ public class GameManager(IGameRepository gameRepository, IHubContext<GameHubSock
         {
             Players = game?.Players,
             CurrentField = game?.Field.CurrentField,
-            State = game?.State
+            State = game?.State,
+            CurrentTurn = game?.CurrentTurn ?? 0
         };
 
         await hubContext.Clients.Client(playerConnectionId).SendAsync("GameInformation", gameInfoDto);
@@ -57,6 +58,9 @@ public class GameManager(IGameRepository gameRepository, IHubContext<GameHubSock
         if (player == null)
             return;
 
+        if(game.CurrentTurn != player.PlayerTag) 
+            return;
+
         var result = game.Field.Drop(column, player.PlayerTag);
 
         if (result != DropResult.Placed)
@@ -92,6 +96,8 @@ public class GameManager(IGameRepository gameRepository, IHubContext<GameHubSock
 
             ScheduleGameDeletion(game.Id, TimeSpan.FromSeconds(5));
         }
+
+        game.CurrentTurn = game.CurrentTurn == 1 ? 2 : 1;
     }
 
     public Task DisconnectedPlayer(string playerConnectionId)