Add dithering for gradients

src/renderer/renderer_dx12.cpp

@@ -148,6 +148,10 @@ float4 PSMain(PSInput input) : SV_TARGET {
         }
     }
 
+    // Dither to reduce gradient banding (interleaved gradient noise)
+    float dither = frac(52.9829189 * frac(dot(input.pos.xy, float2(0.06711056, 0.00583715)))) - 0.5;
+    col.rgb += dither / 255.0;
+
     if (col.a < 0.002) discard;
     return col;
 }