fix: enable imageCubeArray feature + transition all 24 shadow layers

Two validation errors fixed:
1. imageCubeArray feature not enabled → added VkPhysicalDeviceImageCubeArrayFeatures
   to device creation chain (pNext: cubeArray → sync2 → dynamicRendering)
2. Shadow layers 18-23 in UNDEFINED layout → transition ALL 24 layers
   (MaxShadowLights * 6) instead of only numShadowLights * 6
   Descriptor references all 24 layers via CubeArray view

src/Engine.Graphics.Vulkan/VulkanContext.cs

@@ -305,10 +305,17 @@ internal sealed unsafe class VulkanContext : IDisposable
             synchronization2 = VkBool32.True,
         };
 
+        var cubeArrayFeatures = new VkPhysicalDeviceImageCubeArrayFeatures
+        {
+            sType = VkStructureType.PhysicalDeviceImageCubeArrayFeatures,
+            pNext = (nint)(&sync2Features),
+            imageCubeArray = VkBool32.True,
+        };
+
         var renderingFeatures = new VkPhysicalDeviceDynamicRenderingFeatures
         {
             sType = VkStructureType.PhysicalDeviceDynamicRenderingFeatures,
-            pNext = (nint)(&sync2Features),
+            pNext = (nint)(&cubeArrayFeatures),
             dynamicRendering = VkBool32.True,
         };