Fade from main menu to gameplay

src/states/State.h

@@ -55,6 +55,7 @@ struct StateContext {
     std::function<void(bool)> applyFullscreen; // Allows states to request fullscreen changes
     std::function<bool()> queryFullscreen; // Optional callback if fullscreenFlag is not reliable
     std::function<void()> requestQuit; // Allows menu/option states to close the app gracefully
+    std::function<void()> startPlayTransition; // Optional fade hook when transitioning from menu to gameplay
     // Pointer to the application's StateManager so states can request transitions
     StateManager* stateManager = nullptr;
 };