feat(editor): height scale tool for terrain relief control

- Scale Heights: multiply all terrain heights by a factor (0.1x - 5.0x)
- >1.0 exaggerates relief (deeper valleys, taller peaks)
- <1.0 flattens terrain toward base height
- Re-stitches all chunk edges after scaling for seamless results
- Workflow: noise → smooth → scale → clamp for precise control

tools/editor/terrain_editor.hpp

@@ -60,6 +60,9 @@ public:
     // Clamp all heights to a min/max range
     void clampHeights(float minH, float maxH);
 
+    // Scale all heights by a factor (useful for exaggerating or flattening)
+    void scaleHeights(float factor);
+
     // Import/export heightmap (raw 16-bit grayscale, 129x129)
     bool importHeightmap(const std::string& path, float heightScale);
     bool exportHeightmap(const std::string& path, float heightScale);