refactor: implement singleton pattern for key managers and improve resource access

scripts/components/ExitDoorComponent.cs

@@ -1,5 +1,4 @@
 using Godot;
-using Mr.BrickAdventures;
 using Mr.BrickAdventures.Autoloads;
 using Mr.BrickAdventures.scripts.interfaces;
 using Mr.BrickAdventures.scripts.State;
@@ -17,14 +16,8 @@ public partial class ExitDoorComponent : Area2D, IUnlockable
 
     [Signal] public delegate void ExitTriggeredEventHandler();
 
-    private GameManager _gameManager;
-    private AchievementManager _achievementManager;
-
     public override void _Ready()
     {
-        _gameManager = GameManager.Instance;
-        _achievementManager = GetNode<AchievementManager>(Constants.AchievementManagerPath);
-
         BodyEntered += OnExitAreaBodyEntered;
 
     }
@@ -34,10 +27,9 @@ public partial class ExitDoorComponent : Area2D, IUnlockable
         if (Locked) return;
 
         EmitSignalExitTriggered();
-        _achievementManager.UnlockAchievement(AchievementId);
-        // Get current level from GameStateStore
+        AchievementManager.Instance?.UnlockAchievement(AchievementId);
         var currentLevel = GameStateStore.Instance?.Session.CurrentLevel ?? 0;
-        _gameManager.UnlockLevel(currentLevel + 1);
+        GameManager.Instance?.UnlockLevel(currentLevel + 1);
         CallDeferred(nameof(GoToNextLevel));
     }
 
@@ -54,6 +46,6 @@ public partial class ExitDoorComponent : Area2D, IUnlockable
 
     private void GoToNextLevel()
     {
-        _gameManager.OnLevelComplete();
+        GameManager.Instance?.OnLevelComplete();
     }
 }