fix: force B8G8R8A8_UNORM swapchain — fixes acid video colors

Root cause: driver returned format=58 (A2B10G10R10_PACK32) as fallback
when B8G8R8A8_SRGB wasn't found. 10-bit packed format has different
byte layout → vkCmdCopyImageToBuffer gives garbage when interpreted as
8-bit BGRA → acid colors in video.

Fix:
- QuerySurfaceFormat: try B8G8R8A8_UNORM first (NVIDIA supports it)
- Fallback: B8G8R8A8_SRGB, then first available
- Removed SRGB LUT conversion — UNORM data is already linear
- Raw BGRA bytes go directly to FFmpeg (pixel_format=bgra)

src/Engine.Graphics.Vulkan/VulkanRenderer.cs

@@ -149,35 +149,9 @@ public sealed unsafe class VulkanRenderer : IRenderer, Engine.Graphics.IScreensh
         Marshal.Copy((nint)pData, result, 0, (int)_screenshotBufferSize);
         Vk.vkUnmapMemory(_ctx.Device, _screenshotMemory);
 
-        // Swapchain is B8G8R8A8_SRGB — raw bytes are SRGB-encoded
-        // Convert SRGB→linear for FFmpeg (which expects linear bgra)
-        for (int i = 0; i < result.Length; i += 4)
-        {
-            result[i] = SrgbToLinear(result[i]);     // B
-            result[i + 1] = SrgbToLinear(result[i + 1]); // G
-            result[i + 2] = SrgbToLinear(result[i + 2]); // R
-            // result[i + 3] = A (keep as-is)
-        }
-
         return result;
     }
 
-    private static readonly byte[] SrgbLut = BuildSrgbLut();
-
-    private static byte[] BuildSrgbLut()
-    {
-        var lut = new byte[256];
-        for (int i = 0; i < 256; i++)
-        {
-            float s = i / 255.0f;
-            float l = s <= 0.04045f ? s / 12.92f : MathF.Pow((s + 0.055f) / 1.055f, 2.4f);
-            lut[i] = (byte)Math.Clamp(l * 255.0f, 0, 255);
-        }
-        return lut;
-    }
-
-    private static byte SrgbToLinear(byte srgb) => SrgbLut[srgb];
-
     public void BeginImGuiFrame()
     {
         _imGui?.NewFrame();