Lighting: directional sun shadows from the day/night sun angle

DayNight.SunShadow returns a cell offset opposite the sun's east-west position, longest near sunrise/sunset (low sun) and zero at noon/night, tilted slightly south so shadows fall in front of occluders. LightmapBuilder gains a directional shadow pass (MaxShadowCells length cap, SunShadowStrength darkening); LightmapSystem feeds it the current sun shadow each rebuild. Tests cover SunShadow's day-arc behaviour and the builder's directional darkening.

src/MrGameEng.Graphics/Lighting/LightmapSystems.cs

@@ -15,6 +15,8 @@ public sealed class LightmapSystem : BaseSystem
 {
     private const int RebuildEvery = 6; // ~10 Гц при 60 fps
     private const float NightFloor = 0.18f; // ночь тусклая, но не чёрная (лунный свет)
+    private const float MaxShadowCells = 7f; // макс. длина тени от солнца (на рассвете/закате)
+    private const float SunShadowStrength = 0.5f; // насколько темнеет клетка у основания тени
 
     private readonly Lightmap _lightmap;
     private readonly DayNight _dayNight;
@@ -77,7 +79,9 @@ public sealed class LightmapSystem : BaseSystem
             _lightmap.Height,
             ambient,
             _occluders(),
-            _lights
+            _lights,
+            _dayNight.SunShadow(MaxShadowCells),
+            SunShadowStrength
         );
         _lightmap.Upload();
     }