feat(editor): multi-script entities + asset browser panel

ScriptComponent now holds a list of {name, active} items (Unity
semantics: one entity, many scripts, each with its own enable bit;
component-level active stays as the master switch). ScriptRuntime
reconciles instances by name per entity -- rename/remove destroys
only the affected instances, untouched ones keep ticking. Scenes
persist Script.Items; old single-script key still loads.

AssetBrowserPanel (lightweight Unity Project window): fixed roots
(assets/scenes) as tabs, recursive directory tree, file list with
type filter (models/textures/scenes) and name substring filter,
double-click preloads models/HDRs into the asset caches (path-
deduped). Scene files point to the File menu for now; drag & drop
is a later iteration. Docked with Stats by default in fresh layouts.

App/editor/AssetBrowserPanel.h

@@ -0,0 +1,40 @@
+//
+// AssetBrowserPanel：项目资产浏览器（Unity Project 窗口简化版）。
+//
+// 左侧目录树 + 右侧文件列表（类型过滤 + 名字过滤）。与 AssetManager
+// 的集成点是"双击预热"：model/HDR 进缓存去重（重复双击零成本），
+// .scene 提示走 File 菜单（加载含环境恢复/选中清理等流程，不在面板
+// 重复）。拖拽到视口/Inspector 属后续迭代。
+//
+// 目录每帧扫描：项目级目录条目有限（几十量级），filesystem 迭代开销
+// 可忽略；资产规模上来后再加缓存脏标。
+//
+
+#ifndef HELLOVULKAN_ASSETBROWSERPANEL_H
+#define HELLOVULKAN_ASSETBROWSERPANEL_H
+
+#include "EditorContext.h"
+
+#include <filesystem>
+#include <string>
+
+class AssetBrowserPanel {
+public:
+    void Draw(const EditorContext& ctx);
+
+private:
+    // 目录树节点（递归）；右侧列表画 dir 下的文件
+    void DrawDirTree(const EditorContext& ctx,
+                     const std::filesystem::path& dir);
+    void DrawFileList(const EditorContext& ctx,
+                      const std::filesystem::path& dir);
+
+    // 固定根（下标即身份）：项目资产 / 场景文件
+    int m_Root = 0;
+    // 类型过滤（0 = All；其余见 kTypeNames）
+    int m_TypeFilter = 0;
+    // 名字子串过滤（空 = 不过滤）
+    char m_NameFilter[64] = "";
+};
+
+#endif //HELLOVULKAN_ASSETBROWSERPANEL_H