feat: 添加全局屏幕转场面板

- 新增 ScreenTransitionPanel，支持 fade_in/out、fade_in_white、flash_white、
  wipe_in/out、shutter_in/out 等多种转场效果
- 新增 Screen Transition Panel Prefab 并在 Persistence 场景挂载
- UIManager 启动时自动显示该面板
- BaseYarnCommand 新增对应的 Yarn 全局转场指令

Assets/Scripts/Dialog System/BaseYarnCommand.cs

@@ -57,7 +57,7 @@ namespace AibisDream
             var panel = UIManager.Instance.GetPanel<PlayToolPanel>();
             return panel.FadeOutAsync(duration);
         }
-        
+
         [YarnCommand("fade_in_sync")]
         public static void FadeInSync(float duration = 1)
         {
@@ -72,6 +72,48 @@ namespace AibisDream
             panel.FadeOutSync(duration);
         }
 
+        [YarnCommand("fade_in_white")]
+        public static IEnumerator FadeInWhite(float duration = 1)
+        {
+            var panel = UIManager.Instance.GetPanel<ScreenTransitionPanel>();
+            return panel.FadeInWhiteAsync(duration);
+        }
+
+        [YarnCommand("flash_white")]
+        public static IEnumerator FlashWhite(float duration = 0.2f)
+        {
+            var panel = UIManager.Instance.GetPanel<ScreenTransitionPanel>();
+            return panel.FlashWhite(duration);
+        }
+
+        [YarnCommand("wipe_in")]
+        public static IEnumerator WipeIn(float duration = 0.6f)
+        {
+            var panel = UIManager.Instance.GetPanel<ScreenTransitionPanel>();
+            return panel.WipeInAsync(duration);
+        }
+
+        [YarnCommand("wipe_out")]
+        public static IEnumerator WipeOut(float duration = 0.6f)
+        {
+            var panel = UIManager.Instance.GetPanel<ScreenTransitionPanel>();
+            return panel.WipeOutAsync(duration);
+        }
+
+        [YarnCommand("shutter_in")]
+        public static IEnumerator ShutterIn(float duration = 0.6f)
+        {
+            var panel = UIManager.Instance.GetPanel<ScreenTransitionPanel>();
+            return panel.ShutterInAsync(duration);
+        }
+
+        [YarnCommand("shutter_out")]
+        public static IEnumerator ShutterOut(float duration = 0.6f)
+        {
+            var panel = UIManager.Instance.GetPanel<ScreenTransitionPanel>();
+            return panel.ShutterOutAsync(duration);
+        }
+
         [YarnCommand("show_obj")]
         public static IEnumerator ShowObj(string picName, float duration = 1)
         {