feat(editor): object scatter, camera bookmarks, shortcut hints

- Object scatter tool: place N copies of selected M2/WMO in a radius
  with random rotation and scale range (Min/Max Scale slider)
- Camera bookmarks: F5 saves current position, View > Load Bookmark
  to jump back — useful for working on different parts of a large zone
- Shortcut hints shown at bottom of Object panel
  (G=move, R=rotate, T=scale, Del=remove)
- DragFloatRange2 for min/max scale in scatter UI

tools/editor/object_placer.hpp

@@ -61,6 +61,10 @@ public:
     bool canUndoPlace() const { return !undoStack_.empty(); }
     void undoLastPlace();
 
+    // Scatter: place multiple copies with random offset/rotation
+    void scatter(const glm::vec3& center, float radius, int count,
+                 float minScale, float maxScale);
+
 private:
     uint32_t nextUniqueId();