feat(editor): voronoi cell noise for organic terrain patterns

- Voronoi noise generator: creates cell-like terrain patterns with
  ridge features at cell boundaries (F2-F1 distance field)
- Configurable cell count (5-100) and amplitude
- Toggle between Value noise and Voronoi in the noise generator section
- Creates interesting mesa/plateau formations and organic shapes
- Random cell centers with per-cell height variation

tools/editor/terrain_editor.hpp

@@ -111,6 +111,9 @@ public:
     // Offset all heights by a constant
     void offsetHeights(float amount);
 
+    // Voronoi cell noise — creates cell-like terrain patterns
+    void applyVoronoiNoise(int cellCount, float amplitude, uint32_t seed);
+
     // Fill entire tile with water at a height
     void fillWater(float height, uint16_t liquidType);