feat: dynamic point light on a physics ball — falls and illuminates

- LightBall entity: sphere mesh + DynamicSphere physics + Light.Point
- Renderer reads light position from Transform (not static Light.Position)
  so the light moves with the physics body
- Light intensity 20, range 30, warm color (1.0, 0.9, 0.7)
- Ball falls from y=15, bounces on floor, light follows it
- Renderer: prefers Light+Transform pair for dynamic position, falls back to Light only

src/CortexEngine.App/Program.cs

@@ -268,6 +268,13 @@ class Program
             .Set(new Transform(new Vector3(0, 8, 0), Quaternion.Identity, Vector3.One))
             .Set(Light.Point(new Vector3(0, 8, 0), new Vector3(1.0f, 0.9f, 0.7f), intensity: 15.0f, range: 25.0f));
 
+        var lightSphere = ProceduralMesh.CreateSphere(0.5f, 24, 12, new Vector3(1.0f, 0.9f, 0.7f));
+        world.Entity("LightBall")
+            .Set(new Transform(new Vector3(0, 15, 0), Quaternion.Identity, Vector3.One))
+            .Set(lightSphere)
+            .Set(RigidBody.DynamicSphere(0.5f, mass: 0.5f))
+            .Set(Light.Point(new Vector3(0, 15, 0), new Vector3(1.0f, 0.9f, 0.7f), intensity: 20.0f, range: 30.0f));
+
         var entityCount = 0;
         world.Each((Entity e, ref Transform _) => entityCount++);
         Console.WriteLine($"[Scene] {entityCount} entities: torus knot + 4 dynamic cubes + 3 dynamic spheres + static floor + grid");

src/Engine.Graphics.Vulkan/VulkanRenderer.cs

@@ -77,17 +77,28 @@ internal sealed unsafe class VulkanRenderer : IRenderer, Engine.Graphics.IScreen
             vp = Matrix4x4.CreateLookAt(new Vector3(0, 0, -6), Vector3.Zero, Vector3.UnitY) * proj;
         }
 
-        // Collect point light from ECS (first point light found)
+        // Collect point light from ECS — prefer light attached to a moving entity
         var lightPos = new Vector4(0, 5, 0, 0);
         var lightColor = new Vector4(1, 1, 1, 0);
-        world.Each((Entity e, ref Light l) =>
+        world.Each((Entity e, ref Light l, ref Transform lt) =>
         {
             if (l.IsPoint && lightPos.W == 0)
             {
-                lightPos = new Vector4(l.Position, l.Intensity);
+                lightPos = new Vector4(lt.Position, l.Intensity);
                 lightColor = new Vector4(l.Color, l.Range);
             }
         });
+        if (lightPos.W == 0)
+        {
+            world.Each((Entity e, ref Light l) =>
+            {
+                if (l.IsPoint && lightPos.W == 0)
+                {
+                    lightPos = new Vector4(l.Position, l.Intensity);
+                    lightColor = new Vector4(l.Color, l.Range);
+                }
+            });
+        }
 
         // Pack UBO: mat4 vp (64 bytes) + vec4 lightPos (16) + vec4 lightColor (16) = 96 bytes
         var uboData = stackalloc byte[128];