feat: AI screenshot capture for visual analysis

- Add ScreenshotCapture class to Engine.Graphics using Vulkan image readback.
- Integrate screenshot capture into MeshRenderer; request triggers readback on next frame.
- Add SixLabors.ImageSharp 3.1.11 for PNG encoding (patched for CVE-2025-54575).
- Add capture_screenshot AI command and MCP tool.
- Wire screenshot request into Program.cs with demo command.
- Expose swapchain surface format and image accessor for readback.
- Add Screenshots/ to .gitignore.
- Update CORTEX_ENGINE_ARCHITECTURE.md with MCP, Silk.NET.Vulkan, ImageSharp, and screenshot capture.

src/Engine.Graphics/MeshRenderer.cs

@@ -18,6 +18,7 @@ public sealed unsafe class MeshRenderer : IDisposable
     private readonly VulkanContext _context;
     private readonly Swapchain _swapchain;
     private readonly VulkanPipeline _pipeline;
+    private readonly ScreenshotCapture _screenshot;
     private readonly Dictionary<Entity, MeshBuffers> _buffers = new();
     private CommandPool _commandPool;
     private CommandBuffer[] _commandBuffers = null!;
@@ -48,6 +49,7 @@ public sealed unsafe class MeshRenderer : IDisposable
     {
         _context = context;
         _swapchain = swapchain;
+        _screenshot = new ScreenshotCapture(context, swapchain);
 
         _pipeline = new VulkanPipeline(context, swapchain);
         CreateCommandPool();
@@ -118,6 +120,10 @@ public sealed unsafe class MeshRenderer : IDisposable
         }
     }
 
+    public void RequestScreenshot(string outputPath) => _screenshot.Request(outputPath);
+
+    public bool IsScreenshotRequested => _screenshot.IsRequested;
+
     public void RenderWorld(World world)
     {
         var frame = _currentFrame % 2;
@@ -198,6 +204,10 @@ public sealed unsafe class MeshRenderer : IDisposable
         });
 
         _context.Vk.CmdEndRenderPass(cmd);
+
+        var swapchainImage = _swapchain.GetImage(imageIndex);
+        _screenshot.RecordReadback(cmd, swapchainImage, _swapchain.Extent.Width, _swapchain.Extent.Height, _swapchain.SurfaceFormat);
+
         _context.Vk.EndCommandBuffer(cmd);
 
         var waitSemaphore = _imageAvailableSemaphores[frame];
@@ -229,6 +239,14 @@ public sealed unsafe class MeshRenderer : IDisposable
         };
 
         _context.KhrSwapchain!.QueuePresent(_context.PresentQueue, &presentInfo);
+
+        // If a screenshot was requested, wait for the GPU to finish the readback and save the file.
+        if (_screenshot.IsRequested)
+        {
+            _context.Vk.WaitForFences(_context.Device, 1, &fence, true, ulong.MaxValue);
+            _screenshot.Save(_swapchain.Extent.Width, _swapchain.Extent.Height, _swapchain.SurfaceFormat);
+        }
+
         _currentFrame++;
     }
 
@@ -308,6 +326,8 @@ public sealed unsafe class MeshRenderer : IDisposable
     {
         _context.Vk.DeviceWaitIdle(_context.Device);
 
+        _screenshot.Dispose();
+
         foreach (var buffers in _buffers.Values)
             buffers.Dispose();
         _buffers.Clear();