fix: Remove duplicate constants and add null check for updatePhysicsObjects

js/elements/physics_objects.js

@@ -1,7 +1,5 @@
 // Physics objects (square, circle, triangle)
-const SQUARE = 16;
-const CIRCLE = 17;
-const TRIANGLE = 18;
+// Constants are already defined in constants.js
 
 // Physics object properties
 const PHYSICS_OBJECT_COLORS = ['#FF5733', '#33FF57', '#3357FF', '#F3FF33', '#FF33F3'];