feat(core): add cave-generation and fog tuning to Configuration

VoxelEngine.Tests/ConfigurationTests.cs

@@ -54,4 +54,24 @@ public class ConfigurationTests
         Assert.Equal(800,  c2.WindowWidth);
         Assert.Equal(600,  c2.WindowHeight);
     }
+
+    [Fact]
+    public void Defaults_HaveCaveTuningConstants()
+    {
+        var c = new Configuration();
+
+        // Algorithm
+        Assert.Equal(0.03f, c.CaveNoiseFrequency);
+        Assert.Equal(-0.3f, c.CaveNoiseThreshold);
+        Assert.Equal(64,    c.WormCellSize);
+        Assert.Equal(300,   c.WormSpawnProbabilityPermille);
+        Assert.Equal(80,    c.WormMaxLength);
+        Assert.Equal(1.5f,  c.WormMinRadius);
+        Assert.Equal(3.5f,  c.WormMaxRadius);
+
+        // Lighting (fog)
+        Assert.Equal(72f,   c.CaveDarkStartY);    // SeaLevel (64) + 8
+        Assert.Equal(32f,   c.CaveDarkEndY);      // SeaLevel (64) - 32
+        Assert.Equal(0.15f, c.CaveMinBrightness);
+    }
 }