feat(editor): stamp persistence, WCP file preview, enriched stats

- Terrain stamps save/load to JSON: reuse terrain features across zones
  and sessions. Save/Load buttons in Sculpt > Stamp/Clone panel
- WCP Inspect now shows full file breakdown: terrain/model/building/
  texture/data counts with total size. Powered by readInfo file list
  parsing with auto-categorization by extension
- stats.json now includes chunk count, triangle count, tile count, and
  editor version alongside existing object/NPC/quest/texture counts
- Fix unprotected std::stoi in custom zone WOT filename parser

tools/editor/terrain_editor.hpp

@@ -77,6 +77,8 @@ public:
     // Terrain stamp: copy heights from source area, paste at destination
     void copyStamp(const glm::vec3& center, float radius);
     void pasteStamp(const glm::vec3& center);
+    bool saveStamp(const std::string& path) const;
+    bool loadStamp(const std::string& path);
     bool hasStamp() const { return !stampData_.empty(); }
 
     // Mirror terrain along X or Y axis through tile center