fix: sphere collider matches visual size — create at radius 0.5

Root cause: CreateSphere(r) baked scale into mesh radius, then Transform
applied scale again → double scaling. Visual radius was scale*0.5*scale
but collider was scale*0.5.

Fix: always create sphere at radius 0.5 (unit sphere, like cube.obj).
Scale is applied through Transform only. Collider radius = maxScale*0.5
matches visual radius = 0.5 * scale.

src/Engine.AI/AiCommandProcessor.cs

@@ -85,8 +85,7 @@ public sealed class AiCommandProcessor
         Mesh mesh;
         if (isSphere)
         {
-            var r = MathF.Max(MathF.Max(command.Scale.X, command.Scale.Y), command.Scale.Z) * 0.5f;
-            mesh = ProceduralMesh.CreateSphere(r, 24, 12, new Vector3(0.5f, 0.6f, 0.9f));
+            mesh = ProceduralMesh.CreateSphere(0.5f, 24, 12, new Vector3(0.5f, 0.6f, 0.9f));
         }
         else
         {