fix: VK_INDEX_TYPE_UINT32 (was UINT16) + remove unused depth from pipeline

- vkCmdBindIndexBuffer indexType changed from 0 (UINT16) to 1 (UINT32)
  to match uint[] index data — this was causing black screen
- Removed depth stencil state, depth attachment format, and depth
  rendering attachment from pipeline/renderer (depth buffer still
  created in swapchain but unused)

src/Engine.Graphics.Vulkan/Shaders/triangle.frag

@@ -1,11 +1,8 @@
 #version 450
 
 layout(location = 0) in vec3 fragColor;
-layout(location = 1) in vec3 fragNormal;
 layout(location = 0) out vec4 outColor;
 
 void main() {
-    vec3 lightDir = normalize(vec3(0.5, 0.8, 0.3));
-    float diff = max(dot(normalize(fragNormal), lightDir), 0.2);
-    outColor = vec4(fragColor * diff, 1.0);
+    outColor = vec4(fragColor, 1.0);
 }