feat: Step 3 Flecs.NET ECS integration with animated triangle

- Add Transform component and ECS world in Engine.Core.
- TriangleRenderer.RenderWorld queries entities and applies transforms.
- Animate a single triangle entity in Program.cs.
- Pin ppy.SDL3-CS to 2026.520.0 and add linux-x64 RID for bundled native SDL3.
- Add Flecs.NET.Debug/Release 4.0.4-build.546 per configuration.
- Update SDL3 API usage for the 2026.520.0 binding.
- Update architecture file to Silk.NET.Vulkan and Flecs 4.0.4.

src/Engine.Graphics/Engine.Graphics.csproj

@@ -20,6 +20,8 @@
   <ItemGroup>
     <PackageReference Include="Silk.NET.Vulkan" Version="2.21.0" />
     <PackageReference Include="Silk.NET.Vulkan.Extensions.KHR" Version="2.21.0" />
+    <PackageReference Include="Flecs.NET.Debug" Version="4.0.4-build.546" Condition="'$(Configuration)' == 'Debug'" />
+    <PackageReference Include="Flecs.NET.Release" Version="4.0.4-build.546" Condition="'$(Configuration)' == 'Release'" />
   </ItemGroup>
 
   <ItemGroup>

src/Engine.Graphics/TriangleRenderer.cs

@@ -1,12 +1,15 @@
 using System;
+using System.Numerics;
+using Flecs.NET.Core;
 using Silk.NET.Core;
 using Silk.NET.Vulkan;
+using Engine.Core.Components;
 
 namespace Engine.Graphics;
 
 /// <summary>
 /// Renders a colored triangle using a vertex buffer and a simple graphics pipeline.
-/// Uses Silk.NET.Vulkan.
+/// Uses Silk.NET.Vulkan and reads entity transforms from the ECS world.
 /// </summary>
 public sealed unsafe class TriangleRenderer : IDisposable
 {
@@ -115,7 +118,7 @@ public sealed unsafe class TriangleRenderer : IDisposable
         }
     }
 
-    public void RenderFrame()
+    public void RenderWorld(World world)
     {
         var frame = _currentFrame % 2;
 
@@ -160,7 +163,14 @@ public sealed unsafe class TriangleRenderer : IDisposable
         var vertexBuffer = _vertexBuffer.Buffer;
         var offset = 0ul;
         _context.Vk.CmdBindVertexBuffers(cmd, 0, 1, &vertexBuffer, &offset);
-        _context.Vk.CmdDraw(cmd, 3, 1, 0, 0);
+
+        var drawCmd = cmd;
+        world.Each((Entity e, ref Transform transform) =>
+        {
+            var bytes = BuildTriangleVertices(transform);
+            _vertexBuffer.Update(bytes);
+            _context.Vk.CmdDraw(drawCmd, 3, 1, 0, 0);
+        });
 
         _context.Vk.CmdEndRenderPass(cmd);
         _context.Vk.EndCommandBuffer(cmd);
@@ -197,6 +207,39 @@ public sealed unsafe class TriangleRenderer : IDisposable
         _currentFrame++;
     }
 
+    private byte[] BuildTriangleVertices(Transform transform)
+    {
+        var matrix = transform.GetMatrix();
+        var positions = new Vector3[]
+        {
+            new Vector3(0.0f, -0.5f, 0.0f),
+            new Vector3(0.5f, 0.5f, 0.0f),
+            new Vector3(-0.5f, 0.5f, 0.0f)
+        };
+        var colors = new[]
+        {
+            new Vector3(1.0f, 0.0f, 0.0f),
+            new Vector3(0.0f, 1.0f, 0.0f),
+            new Vector3(0.0f, 0.0f, 1.0f)
+        };
+
+        var bytes = new byte[3 * 5 * sizeof(float)];
+        fixed (byte* p = bytes)
+        {
+            var dst = (float*)p;
+            for (var i = 0; i < 3; i++)
+            {
+                var transformed = Vector3.Transform(positions[i], matrix);
+                dst[i * 5 + 0] = transformed.X;
+                dst[i * 5 + 1] = transformed.Y;
+                dst[i * 5 + 2] = colors[i].X;
+                dst[i * 5 + 3] = colors[i].Y;
+                dst[i * 5 + 4] = colors[i].Z;
+            }
+        }
+        return bytes;
+    }
+
     public void Dispose()
     {
         _context.Vk.DeviceWaitIdle(_context.Device);

src/Engine.Graphics/VertexBuffer.cs

@@ -102,6 +102,14 @@ public sealed unsafe class VertexBuffer : IDisposable
         _context.Vk.UnmapMemory(_context.Device, Memory);
     }
 
+    public void Update(ReadOnlySpan<byte> data)
+    {
+        if ((ulong)data.Length != Size)
+            throw new ArgumentException($"Vertex buffer update size mismatch: {data.Length} != {Size}");
+
+        CopyData(data);
+    }
+
     public void Dispose()
     {
         _context.Vk.DeviceWaitIdle(_context.Device);