feat: add depth buffer, camera and MVP push constants

- Add Camera ECS component with view/projection matrices.
- Add Vulkan depth buffer to Swapchain: image, memory, view, render pass, framebuffers.
- Update VulkanPipeline with depth stencil testing and push-constant layout.
- Update vertex shader to use push-constant MVP matrix.
- MeshRenderer finds Camera, computes MVP per entity and pushes it.
- Program.cs creates a camera entity and keeps the cube rotating.

Build and run verified: window opens and FPS is reported.

src/Engine.Graphics/Swapchain.cs

@@ -17,6 +17,10 @@ public sealed unsafe class Swapchain : IDisposable
     private Image[] _images = null!;
     private ImageView[] _imageViews = null!;
     private Framebuffer[] _framebuffers = null!;
+    private Image _depthImage;
+    private DeviceMemory _depthMemory;
+    private ImageView _depthImageView;
+    private Format _depthFormat;
     private SurfaceFormatKHR _surfaceFormat;
     private PresentModeKHR _presentMode;
     private Extent2D _extent;
@@ -31,6 +35,7 @@ public sealed unsafe class Swapchain : IDisposable
     {
         _context = context;
         _surfaceFormat = ChooseSurfaceFormat();
+        _depthFormat = FindDepthFormat();
         CreateRenderPass();
         Recreate(1280, 720);
     }
@@ -77,6 +82,8 @@ public sealed unsafe class Swapchain : IDisposable
         _imageViews = new ImageView[_images.Length];
         _framebuffers = new Framebuffer[_images.Length];
 
+        CreateDepthResources();
+
         for (var i = 0; i < _images.Length; i++)
         {
             _imageViews[i] = CreateImageView(_images[i], _surfaceFormat.Format);
@@ -107,6 +114,113 @@ public sealed unsafe class Swapchain : IDisposable
         return images;
     }
 
+    private Format FindDepthFormat()
+    {
+        var candidates = new[] { Format.D32Sfloat, Format.D32SfloatS8Uint, Format.D24UnormS8Uint };
+        foreach (var format in candidates)
+        {
+            FormatProperties props;
+            _context.Vk.GetPhysicalDeviceFormatProperties(_context.PhysicalDevice, format, &props);
+            if ((props.OptimalTilingFeatures & FormatFeatureFlags.DepthStencilAttachmentBit) != 0)
+                return format;
+        }
+        throw new InvalidOperationException("No supported depth format found.");
+    }
+
+    private uint FindMemoryType(uint typeFilter, MemoryPropertyFlags properties)
+    {
+        PhysicalDeviceMemoryProperties memoryProperties;
+        _context.Vk.GetPhysicalDeviceMemoryProperties(_context.PhysicalDevice, &memoryProperties);
+        for (var i = 0; i < memoryProperties.MemoryTypeCount; i++)
+        {
+            if ((typeFilter & (1u << i)) != 0 &&
+                (memoryProperties.MemoryTypes[i].PropertyFlags & properties) == properties)
+            {
+                return (uint)i;
+            }
+        }
+        throw new InvalidOperationException("Failed to find suitable memory type.");
+    }
+
+    private void CreateDepthResources()
+    {
+        CreateDepthImage();
+        CreateDepthImageView();
+    }
+
+    private void CreateDepthImage()
+    {
+        var createInfo = new ImageCreateInfo
+        {
+            SType = StructureType.ImageCreateInfo,
+            ImageType = ImageType.Type2D,
+            Extent = new Extent3D(_extent.Width, _extent.Height, 1),
+            MipLevels = 1,
+            ArrayLayers = 1,
+            Format = _depthFormat,
+            Tiling = ImageTiling.Optimal,
+            InitialLayout = ImageLayout.Undefined,
+            Usage = ImageUsageFlags.DepthStencilAttachmentBit,
+            Samples = SampleCountFlags.Count1Bit,
+            SharingMode = SharingMode.Exclusive
+        };
+
+        Image image;
+        var result = _context.Vk.CreateImage(_context.Device, &createInfo, null, &image);
+        if (result != Result.Success)
+            throw new InvalidOperationException($"vkCreateImage failed: {result}");
+        _depthImage = image;
+
+        MemoryRequirements memRequirements;
+        _context.Vk.GetImageMemoryRequirements(_context.Device, image, &memRequirements);
+
+        var memoryTypeIndex = FindMemoryType(memRequirements.MemoryTypeBits, MemoryPropertyFlags.DeviceLocalBit);
+        var allocInfo = new MemoryAllocateInfo
+        {
+            SType = StructureType.MemoryAllocateInfo,
+            AllocationSize = memRequirements.Size,
+            MemoryTypeIndex = memoryTypeIndex
+        };
+
+        DeviceMemory memory;
+        result = _context.Vk.AllocateMemory(_context.Device, &allocInfo, null, &memory);
+        if (result != Result.Success)
+            throw new InvalidOperationException($"vkAllocateMemory failed: {result}");
+        _depthMemory = memory;
+
+        result = _context.Vk.BindImageMemory(_context.Device, image, memory, 0);
+        if (result != Result.Success)
+            throw new InvalidOperationException($"vkBindImageMemory failed: {result}");
+    }
+
+    private void CreateDepthImageView()
+    {
+        var createInfo = new ImageViewCreateInfo
+        {
+            SType = StructureType.ImageViewCreateInfo,
+            Image = _depthImage,
+            ViewType = ImageViewType.Type2D,
+            Format = _depthFormat,
+            SubresourceRange = new ImageSubresourceRange(ImageAspectFlags.DepthBit, 0, 1, 0, 1)
+        };
+
+        ImageView imageView;
+        var result = _context.Vk.CreateImageView(_context.Device, &createInfo, null, &imageView);
+        if (result != Result.Success)
+            throw new InvalidOperationException($"vkCreateImageView failed: {result}");
+        _depthImageView = imageView;
+    }
+
+    private void CleanupDepthResources()
+    {
+        if (_depthImageView.Handle != 0)
+            _context.Vk.DestroyImageView(_context.Device, _depthImageView, null);
+        if (_depthImage.Handle != 0)
+            _context.Vk.DestroyImage(_context.Device, _depthImage, null);
+        if (_depthMemory.Handle != 0)
+            _context.Vk.FreeMemory(_context.Device, _depthMemory, null);
+    }
+
     private void CreateRenderPass()
     {
         var colorAttachment = new AttachmentDescription
@@ -121,17 +235,38 @@ public sealed unsafe class Swapchain : IDisposable
             FinalLayout = ImageLayout.PresentSrcKhr
         };
 
+        var depthAttachment = new AttachmentDescription
+        {
+            Format = _depthFormat,
+            Samples = SampleCountFlags.Count1Bit,
+            LoadOp = AttachmentLoadOp.Clear,
+            StoreOp = AttachmentStoreOp.DontCare,
+            StencilLoadOp = AttachmentLoadOp.DontCare,
+            StencilStoreOp = AttachmentStoreOp.DontCare,
+            InitialLayout = ImageLayout.Undefined,
+            FinalLayout = ImageLayout.DepthStencilAttachmentOptimal
+        };
+
+        var attachments = new[] { colorAttachment, depthAttachment };
+
         var colorAttachmentRef = new AttachmentReference
         {
             Attachment = 0,
             Layout = ImageLayout.ColorAttachmentOptimal
         };
 
+        var depthAttachmentRef = new AttachmentReference
+        {
+            Attachment = 1,
+            Layout = ImageLayout.DepthStencilAttachmentOptimal
+        };
+
         var subpass = new SubpassDescription
         {
             PipelineBindPoint = PipelineBindPoint.Graphics,
             ColorAttachmentCount = 1,
-            PColorAttachments = &colorAttachmentRef
+            PColorAttachments = &colorAttachmentRef,
+            PDepthStencilAttachment = &depthAttachmentRef
         };
 
         var dependency = new SubpassDependency
@@ -144,22 +279,25 @@ public sealed unsafe class Swapchain : IDisposable
             DstAccessMask = AccessFlags.ColorAttachmentWriteBit
         };
 
-        var createInfo = new RenderPassCreateInfo
+        fixed (AttachmentDescription* pAttachments = attachments)
         {
-            SType = StructureType.RenderPassCreateInfo,
-            AttachmentCount = 1,
-            PAttachments = &colorAttachment,
-            SubpassCount = 1,
-            PSubpasses = &subpass,
-            DependencyCount = 1,
-            PDependencies = &dependency
-        };
+            var createInfo = new RenderPassCreateInfo
+            {
+                SType = StructureType.RenderPassCreateInfo,
+                AttachmentCount = (uint)attachments.Length,
+                PAttachments = pAttachments,
+                SubpassCount = 1,
+                PSubpasses = &subpass,
+                DependencyCount = 1,
+                PDependencies = &dependency
+            };
 
-        RenderPass renderPass;
-        var result = _context.Vk.CreateRenderPass(_context.Device, &createInfo, null, &renderPass);
-        if (result != Result.Success)
-            throw new InvalidOperationException($"vkCreateRenderPass failed: {result}");
-        _renderPass = renderPass;
+            RenderPass renderPass;
+            var result = _context.Vk.CreateRenderPass(_context.Device, &createInfo, null, &renderPass);
+            if (result != Result.Success)
+                throw new InvalidOperationException($"vkCreateRenderPass failed: {result}");
+            _renderPass = renderPass;
+        }
     }
 
     private ImageView CreateImageView(Image image, Format format)
@@ -183,22 +321,26 @@ public sealed unsafe class Swapchain : IDisposable
 
     private Framebuffer CreateFramebuffer(ImageView imageView)
     {
-        var createInfo = new FramebufferCreateInfo
+        var attachments = new[] { imageView, _depthImageView };
+        fixed (ImageView* pAttachments = attachments)
         {
-            SType = StructureType.FramebufferCreateInfo,
-            RenderPass = _renderPass,
-            AttachmentCount = 1,
-            PAttachments = &imageView,
-            Width = _extent.Width,
-            Height = _extent.Height,
-            Layers = 1
-        };
+            var createInfo = new FramebufferCreateInfo
+            {
+                SType = StructureType.FramebufferCreateInfo,
+                RenderPass = _renderPass,
+                AttachmentCount = (uint)attachments.Length,
+                PAttachments = pAttachments,
+                Width = _extent.Width,
+                Height = _extent.Height,
+                Layers = 1
+            };
 
-        Framebuffer framebuffer;
-        var result = _context.Vk.CreateFramebuffer(_context.Device, &createInfo, null, &framebuffer);
-        if (result != Result.Success)
-            throw new InvalidOperationException($"vkCreateFramebuffer failed: {result}");
-        return framebuffer;
+            Framebuffer framebuffer;
+            var result = _context.Vk.CreateFramebuffer(_context.Device, &createInfo, null, &framebuffer);
+            if (result != Result.Success)
+                throw new InvalidOperationException($"vkCreateFramebuffer failed: {result}");
+            return framebuffer;
+        }
     }
 
     private SurfaceFormatKHR ChooseSurfaceFormat()
@@ -275,6 +417,8 @@ public sealed unsafe class Swapchain : IDisposable
             }
         }
 
+        CleanupDepthResources();
+
         if (_imageViews != null)
         {
             foreach (var view in _imageViews)