fix: ImGui font upload barriers — use correct sync2 access flags

0x2000 was VK_ACCESS_MEMORY_READ_BIT in Vulkan 1.0 but maps to
VK_ACCESS_2_HOST_READ_BIT in sync2. Replaced with 0x1000
(VK_ACCESS_2_TRANSFER_WRITE_BIT) for dst access on transfer layout.

src/Engine.Graphics.Vulkan/VulkanImGui.cs

@@ -120,7 +120,7 @@ internal sealed unsafe class VulkanImGui : IDisposable
         var cmd = BeginOneTimeCommands();
         TransitionImageLayoutCmd(cmd, _fontImage,
             VkImageLayout.Undefined, VkImageLayout.TransferDstOptimal,
-            0, 0, 0x1000, 0x2000);
+            0, 0, 0x1000, 0x1000);
 
         var region = new VkBufferImageCopyRegion
         {
@@ -141,7 +141,7 @@ internal sealed unsafe class VulkanImGui : IDisposable
 
         TransitionImageLayoutCmd(cmd, _fontImage,
             VkImageLayout.TransferDstOptimal, VkImageLayout.ShaderReadOnlyOptimal,
-            0x1000, 0x2000, 0x8, 0x20);
+            0x1000, 0x1000, 0x8, 0x20);
 
         EndOneTimeCommands(cmd);