feat: complete client integration for all 6 open formats

- Wire WOB buildings into WMO render pipeline (loads→converts→renders)
- Implement JSON DBC loading in DBCFile::loadJSON() with nlohmann/json
- Wire JSON DBC override into AssetManager (custom_zones/output scan)
- Add WMO→WOB conversion with full geometry (fromWMO)
- Replace placeholder WOB export with real WMO→WOB conversion in editor
- Add --convert-wmo CLI flag for batch WMO→WOB conversion
- Store discovered custom zones on Renderer with getCustomZones() accessor
- Add isCustomZone_ member to TerrainManager

All 6 Blizzard format replacements now fully load in the client:
  ADT→WOT/WHM, WDT→zone.json, BLP→PNG, DBC→JSON, M2→WOM, WMO→WOB

include/pipeline/dbc_loader.hpp

@@ -149,6 +149,8 @@ private:
      * Rebuilds the same in-memory layout as binary load.
      */
     bool loadCSV(const std::vector<uint8_t>& csvData);
+
+    bool loadJSON(const std::vector<uint8_t>& jsonData);
 };
 
 /**