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.cpp

@@ -0,0 +1,23 @@
+#include "ProjectManager.h"
+
+namespace UI {
+
+ProjectManager& ProjectManager::Get() {
+    static ProjectManager instance;
+    return instance;
+}
+
+void ProjectManager::CreateDemoAssets() {
+    m_items = {
+        {"Cube", "Prefab", false},
+        {"Sphere", "Prefab", false},
+        {"Player", "Prefab", false},
+        {"MainScript", "Script", false},
+        {"DefaultMat", "Material", false},
+        {"Scene1", "Scene", false},
+        {"Textures", "Folder", true},
+        {"Models", "Folder", true},
+    };
+}
+
+}