feat(world-gen): larger biomes, smooth height blending, capped mountains; centralize tunables in Configuration

Terrain feel: biome regions ~10x larger (Voronoi cell size 96->960); terrain height now eases across biome borders via a Voronoi distance blend (smooth, and ~25x cheaper than the old 169-sample box blur); mountains capped to ~2/3 world height and gentled (ridged amplitude/frequency lowered), snow line lowered to match.

Centralization: ~27 world-gen/render tuning constants (biome amplitudes & frequencies, climate-noise frequencies/octaves, biome-selection thresholds, blend width, cell size, filler depth, snow line, camera near plane, spawn offset, overlay scale) hoisted from scattered literals into a region-organized, fully-commented Configuration. Configuration is threaded into NoiseSource, the biomes, BiomeRegistry, BiomeMap (+Classify), TerrainSampler, WorldGenerator (+BlockAt filler depth), and Camera via Player. Defaults equal the prior values, so generation is unchanged; worldgen tests updated for the new constructor signatures.

Rendering/Camera.cs

@@ -10,6 +10,7 @@ public sealed class Camera
     public float Yaw { get; private set; } = -90f;   // degrees; -90 looks down -Z
     public float Pitch { get; private set; }         // degrees
     public float Fov { get; set; } = 60f;            // degrees
+    public float NearPlane { get; set; } = 0.1f;     // world units
     public float FarPlane { get; set; } = 100f;      // world units
     public float AspectRatio { get; set; }
 
@@ -37,7 +38,7 @@ public sealed class Camera
 
     public Matrix4 GetProjectionMatrix() =>
         Matrix4.CreatePerspectiveFieldOfView(
-            MathHelper.DegreesToRadians(this.Fov), this.AspectRatio, 0.1f, this.FarPlane);
+            MathHelper.DegreesToRadians(this.Fov), this.AspectRatio, this.NearPlane, this.FarPlane);
 
     private void UpdateVectors()
     {
@@ -49,7 +50,7 @@ public sealed class Camera
             MathF.Sin(pitch),
             MathF.Sin(yaw) * MathF.Cos(pitch)));
 
-        this.Right = Vector3.Normalize(Vector3.Cross(this.Front, Camera.WorldUp));
+        this.Right = Vector3.Normalize(Vector3.Cross(this.Front, WorldUp));
         this.Up = Vector3.Normalize(Vector3.Cross(this.Right, this.Front));
     }
 }