feat(scene-mgmt): 添加全屏图片展示功能

新增全屏/大图展示功能，支持 Yarn 命令控制：
- ShowLargeObj: 显示大图并淡入
- HideLargeObj: 隐藏大图并淡出
- HideAll: 同时隐藏大小图
- 实现大小图互斥切换逻辑
- 重构 HideObj 方法支持可选强制隐藏参数

在梦境场景中配置了大图渲染器和游戏对象，
添加相关 Yarn 命令绑定到 Dialog System。

Made-with: Cursor

Assets/Scripts/Dialog System/BaseYarnCommand.cs

@@ -122,6 +122,24 @@ namespace AibisDream
             SpriteShowcase.Instance.FadeOutSync(duration);
         }
 
+        [YarnCommand("show_large_sprite")]
+        public static IEnumerator ShowLargeSprite(string picName, float duration = 1)
+        {
+            yield return SpriteShowcase.Instance.ShowLargeObj(picName, duration);
+        }
+
+        [YarnCommand("hide_large_sprite")]
+        public static IEnumerator HideLargeSprite(float duration = 1)
+        {
+            yield return SpriteShowcase.Instance.HideLargeObj(duration);
+        }
+
+        [YarnCommand("hide_all_sprites")]
+        public static IEnumerator HideAllSprites(float duration = 1)
+        {
+            yield return SpriteShowcase.Instance.HideAll(duration);
+        }
+
         [YarnCommand("show_full_screen")]
         public static IEnumerator ShowFullScreen(string picName)
         {