fix: regenerate all OBJ files with verified CCW winding + remove grid

- pyramid.obj: verified CCW via cross-product for all 6 faces
- diamond.obj: verified CCW for all 8 octahedron faces
- torus.obj: verified CCW — normal points outward from torus center
- cone.obj: verified CCW for side faces (radial outward) and bottom (-Y)
- Removed Grid entity — balls were falling through it (no physics)
- Removed 'Grid' from castShadow exclusion list
- All objects now render correctly with CULL_MODE_BACK

Content/diamond.obj

@@ -1,15 +1,15 @@
 # Diamond (octahedron)
-v 0 0.5 0
-v 0.5 0 -0.5
-v 0.5 0 0.5
-v -0.5 0 0.5
-v -0.5 0 -0.5
-v 0 -0.5 0
+v 0.000000 0.500000 0.000000
+v 0.500000 0.000000 -0.500000
+v 0.500000 0.000000 0.500000
+v -0.500000 0.000000 0.500000
+v -0.500000 0.000000 -0.500000
+v 0.000000 -0.500000 0.000000
 f 1 5 2
 f 1 2 3
 f 1 3 4
 f 1 4 5
-f 6 2 5
-f 6 3 2
-f 6 4 3
-f 6 5 4
+f 6 5 2
+f 6 2 3
+f 6 3 4
+f 6 4 5