Load terrain when entering world in online mode

Add world entry callback that triggers terrain loading when receiving
SMSG_LOGIN_VERIFY_WORLD. Fix coordinate conversion by applying
serverToCanonical() to properly swap X/Y axes from server format.

include/core/application.hpp

@@ -80,6 +80,7 @@ private:
     void spawnNpcs();
     std::string getPlayerModelPath() const;
     static const char* mapIdToName(uint32_t mapId);
+    void loadOnlineWorldTerrain(uint32_t mapId, float x, float y, float z);
 
     static Application* instance;