Fix crash in character creation by deferring callback to next update

The charCreateCallback was firing synchronously during ImGui render,
causing a state transition before the create screen's ImGui::End() was
called. Defer the callback to GameHandler::update() and ensure update()
runs during CHARACTER_CREATION and CHARACTER_SELECTION states.

include/game/game_handler.hpp

@@ -525,6 +525,9 @@ private:
     WorldConnectSuccessCallback onSuccess;
     WorldConnectFailureCallback onFailure;
     CharCreateCallback charCreateCallback_;
+    bool pendingCharCreateResult_ = false;
+    bool pendingCharCreateSuccess_ = false;
+    std::string pendingCharCreateMsg_;
 
     // ---- XP tracking ----
     uint32_t playerXp_ = 0;