rendering: tune main light shadow bias defaults

engine/include/XCEngine/Rendering/Shadow/DirectionalShadowSettings.h

@@ -6,14 +6,18 @@ namespace XCEngine {
 namespace Rendering {
 
 struct DirectionalShadowSamplingSettings {
-    float receiverDepthBias = 0.0015f;
-    float normalBiasScale = 1.5f;
+    // Keep receiver bias modest and rely more on caster / normal bias so
+    // contact shadows do not detach too aggressively.
+    float receiverDepthBias = 0.0010f;
+    float normalBiasScale = 2.0f;
     float shadowStrength = 0.85f;
 };
 
 struct DirectionalShadowCasterBiasSettings {
-    float depthBiasFactor = 1.0f;
-    int32_t depthBiasUnits = 2;
+    // Single-map directional shadows need a stronger raster bias baseline than
+    // the previous placeholder values to keep acne under control.
+    float depthBiasFactor = 2.5f;
+    int32_t depthBiasUnits = 4;
 };
 
 } // namespace Rendering