feat(rendering): distance fog and config-derived far plane

Assets/shaders/chunk.vert

@@ -6,6 +6,7 @@ layout(location = 2) in float aShade;
 out vec2 vUv;
 out float vShade;
 out float vWorldY;
+out vec3 vWorldPos;
 
 uniform mat4 model;
 uniform mat4 view;
@@ -17,6 +18,7 @@ void main()
     vShade = aShade;
     // World-space position uses row-vector convention (matches gl_Position below).
     vec4 worldPos = vec4(aPos, 1.0) * model;
+    vWorldPos = worldPos.xyz;
     vWorldY = worldPos.y;
     gl_Position = worldPos * view * projection;
 }