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/editor_app.hpp

@@ -69,6 +69,7 @@ public:
 
     void startGizmoMode(TransformMode mode);
     void setGizmoAxis(TransformAxis axis);
+    void setSkyPreset(int preset); // 0=day, 1=dusk, 2=night
     void snapSelectedToGround();
 
     // Multi-tile support