feat(角色): 添加角色阴影渲染功能

新增 CharacterShadowActor 类用于处理角色阴影的渲染
在 CharacterObject 中实现阴影的同步和渲染逻辑
移除 GameDebugActor 中不再使用的合成纹理预览代码
添加 EnsureCompositeTextureReady 方法确保纹理准备就绪

Game/include/character/CharacterShadowActor.h

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <frostbite2D/2d/sprite.h>
+
+namespace frostbite2D {
+
+struct CharacterShadowFrameSnapshot {
+  bool visible = false;
+  Ptr<Texture> texture = nullptr;
+  Vec2 textureSize = Vec2::Zero();
+  Vec2 groundAnchorInTexture = Vec2::Zero();
+  Vec2 groundScreenPosition = Vec2::Zero();
+  int zOrder = 0;
+  uint64 textureVersion = 0;
+};
+
+class CharacterShadowActor : public Sprite {
+public:
+  CharacterShadowActor();
+
+  void ApplyFrameSnapshot(const CharacterShadowFrameSnapshot& snapshot);
+
+private:
+  void ApplyTextureState(const CharacterShadowFrameSnapshot& snapshot);
+
+  Ptr<Texture> appliedTexture_ = nullptr;
+  Vec2 appliedTextureSize_ = Vec2::Zero();
+  Vec2 appliedGroundAnchorInTexture_ = Vec2::Zero();
+  uint64 appliedTextureVersion_ = 0;
+};
+
+} // namespace frostbite2D