feat: Add intro splash screen with transition effects and rendering support

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_dart/lib/src/engine/wolf_3d_engine_base.dart

@@ -295,6 +295,9 @@ class WolfEngine {
     }
 
     switch (menuManager.activeMenu) {
+      case WolfMenuScreen.introSplash:
+        menuManager.updateIntroSplash(input);
+        break;
       case WolfMenuScreen.mainMenu:
         _tickMainMenu(input);
         break;
@@ -370,7 +373,7 @@ class WolfEngine {
       _currentEpisodeIndex = 0;
       onEpisodeSelected?.call(null);
       menuManager.clearEpisodeSelection();
-      menuManager.startTransition(WolfMenuScreen.mainMenu);
+      menuManager.beginIntroSplash();
     }
   }