chore: remove all graphics backends (Raylib, OpenTK, Vulkan/Silk.NET) — prepare for pure Vulkan P/Invoke rewrite

src/Engine.Graphics.Vulkan/Shaders/vertex.vert

@@ -1,48 +0,0 @@
-#version 450
-
-layout(location = 0) in vec3 inPosition;
-layout(location = 1) in vec3 inColor;
-layout(location = 2) in vec3 inNormal;
-
-layout(location = 0) out vec3 fragColor;
-layout(location = 1) out vec3 fragNormal;
-layout(location = 2) out vec3 fragWorldPos;
-layout(location = 3) out vec2 fragUv;
-
-struct Light
-{
-    vec3 direction;
-    float intensity;
-    vec3 color;
-    float _pad;
-};
-
-layout(set = 0, binding = 0) uniform FrameConstants
-{
-    vec3 cameraPosition;
-    uint lightCount;
-    vec3 ambientColor;
-    float _pad;
-    Light lights[4];
-} frame;
-
-layout(push_constant) uniform PushConstants
-{
-    mat4 mvp;
-    vec3 materialAlbedo;
-    float materialRoughness;
-    float materialMetallic;
-    uint useTexture;
-    uint textureIndex;
-    uint _pad0;
-    uint _pad1;
-} push;
-
-void main()
-{
-    gl_Position = push.mvp * vec4(inPosition, 1.0);
-    fragColor = inColor;
-    fragNormal = inNormal;
-    fragWorldPos = inPosition;
-    fragUv = inPosition.xz * 0.5 + 0.5;
-}