重构UI架构：分离数据模型和显示逻辑

- 新增 Core 模块：GameObject、LogEntry、AssetItem 数据模型
- 新增 Managers 模块：SceneManager、LogSystem、ProjectManager
- Panel 层只负责显示，不再持有数据
- 解耦 HierarchyPanel 和 InspectorPanel 之间的直接依赖

ui/src/Managers/ProjectManager.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "Core/AssetItem.h"
+#include <vector>
+#include <string>
+
+namespace UI {
+
+class ProjectManager {
+public:
+    static ProjectManager& Get();
+    
+    std::vector<AssetItem>& GetItems() { return m_items; }
+    int GetSelectedIndex() const { return m_selectedIndex; }
+    void SetSelectedIndex(int index) { m_selectedIndex = index; }
+    
+    void CreateDemoAssets();
+
+private:
+    ProjectManager() = default;
+    
+    std::vector<AssetItem> m_items;
+    int m_selectedIndex = -1;
+};
+
+}