feat(editor): procedural noise generator, sky presets, viewport lighting

- Noise Generator in Sculpt panel: applies procedural value noise
  with configurable frequency, amplitude, octaves, and seed
  to create hills/valleys across entire tile instantly
- Sky/Lighting presets: View > Sky menu with Day (blue sky, high sun),
  Dusk (orange, low sun), Night (dark blue, moonlight)
- Viewport clear color and light direction now configurable at runtime
- Noise uses smoothstep interpolation with octave fractal layering

tools/editor/terrain_editor.hpp

@@ -51,6 +51,9 @@ public:
     // Recalculate normals for modified chunks (improves lighting after sculpt)
     void recalcNormals(const std::vector<int>& chunkIndices);
 
+    // Noise generator: applies procedural height noise to the terrain
+    void applyNoise(float frequency, float amplitude, int octaves, uint32_t seed);
+
     // Water editing
     void setWaterLevel(const glm::vec3& center, float radius, float waterHeight, uint16_t liquidType = 0);
     void removeWater(const glm::vec3& center, float radius);