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

src/Engine.Graphics/MeshMath.cs

@@ -1,26 +0,0 @@
-using System.Numerics;
-
-namespace Engine.Graphics;
-
-/// <summary>
-/// Shared mesh math utilities used by loaders and procedural generators.
-/// </summary>
-public static class MeshMath
-{
-    /// <summary>
-    /// Compute a flat face normal from three vertex positions.
-    /// Falls back to Vector3.UnitY for degenerate (zero-area) triangles.
-    /// </summary>
-    public static Vector3 ComputeFaceNormal(Vector3 a, Vector3 b, Vector3 c)
-    {
-        var ab = b - a;
-        var ac = c - a;
-        // Cross(ac, ab) instead of Cross(ab, ac) to match CW winding in typical OBJ files
-        var normal = Vector3.Cross(ac, ab);
-        if (normal.LengthSquared() > 0.00001f)
-            normal = Vector3.Normalize(normal);
-        else
-            normal = Vector3.UnitY;
-        return normal;
-    }
-}