feat(editor): fly-to-object, export README, quality of life

- "Fly To" button on selected objects and NPCs: moves camera 30 units
  above the selected item for quick navigation on large zones
- Export now generates README.txt with zone summary: map name, tile
  coords, object/NPC counts, and file listing
- Complete export package: zone.json + WDT + ADT + objects.json +
  creatures.json + README.txt

tools/editor/editor_app.hpp

@@ -72,6 +72,7 @@ public:
     void setGizmoAxis(TransformAxis axis);
     void setSkyPreset(int preset); // 0=day, 1=dusk, 2=night
     void snapSelectedToGround();
+    void flyToSelected();
 
     // Multi-tile support
     void addAdjacentTile(int offsetX, int offsetY);