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/rendering/terrain_manager.hpp

@@ -201,6 +201,8 @@ public:
      * @param mapName Map name (e.g., "Azeroth", "Kalimdor")
      */
     void setMapName(const std::string& mapName) { this->mapName = mapName; }
+    bool isCustomZone() const { return isCustomZone_; }
+    void setCustomZone(bool custom) { isCustomZone_ = custom; }
 
     /**
      * Load a single tile
@@ -352,6 +354,7 @@ private:
     float timeSinceLastUpdate = 0.0f;
     float proactiveStreamTimer_ = 0.0f;
     bool taxiStreamingMode_ = false;
+    bool isCustomZone_ = false;
 
     // Tile size constants (WoW ADT specifications)
     // A tile (ADT) = 16x16 chunks = 533.33 units across