fix: null guard for unassigned LevelDefinition

Assets/Scripts/Infrastructure/Unity/GameBootstrap.cs

@@ -132,9 +132,12 @@ namespace Infrastructure.Unity
                 // Calculate current floor index based on Y height (inverse logic from Generator)
                 // Note: Generator uses negative offsets: 0, -15, -30.
                 // So Floor 0 is at Y=0. Floor 1 is at Y=-15.
-                
-                var heightDist = levelGenerator.Definition.FloorHeightDistance;
-                var maxFloors = levelGenerator.Definition.FloorCount;
+
+                var def = levelGenerator.Definition;
+                if (def == null) return;
+
+                var heightDist = def.FloorHeightDistance;
+                var maxFloors = def.FloorCount;
     
                 var rawFloor = Mathf.RoundToInt(-playerY / heightDist);
                 _currentPlayerFloorIndex = Mathf.Clamp(rawFloor, 0, maxFloors - 1);