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.

Engine/src/Serialization/SceneSerializer.cpp

@@ -350,12 +350,20 @@ namespace Engine::Serialization {
                 out << YAML::EndMap;
             }
 
-            // 脚本只存类名（注册表键）；未注册名字加载后运行时警告跳过
+            // 脚本：多脚本列表（每项 = 名字 + 独立启停位）；未注册名字
+            // 加载后运行时警告跳过
             if (const auto* sc = reg.try_get<ECS::ScriptComponent>(e)) {
                 out << YAML::Key << "Script" << YAML::Value << YAML::BeginMap;
-                out << YAML::Key << "ScriptName" << YAML::Value
-                    << sc->scriptName;
                 out << YAML::Key << "Active" << YAML::Value << sc->active;
+                out << YAML::Key << "Items" << YAML::Value << YAML::BeginSeq;
+                for (const auto& item : sc->items) {
+                    // flow map 单行一项，与场景格式定案一致
+                    out << YAML::BeginMap;
+                    out << YAML::Key << "Name" << YAML::Value << item.name;
+                    out << YAML::Key << "Active" << YAML::Value << item.active;
+                    out << YAML::EndMap;
+                }
+                out << YAML::EndSeq;
                 out << YAML::EndMap;
             }
 
@@ -655,11 +663,25 @@ namespace Engine::Serialization {
                 // 状态（速度/着地）由 PhysicsWorld 对账重建，不存
             }
 
-            // 脚本：只存类名；未注册名字由 ScriptRuntime 运行时警告跳过
+            // 脚本：优先读多脚本 Items；无 Items 回退旧单脚本键（向前兼容）
             if (const YAML::Node n = comps["Script"]) {
                 auto& sc = handle.AddComponent<ECS::ScriptComponent>();
-                sc.scriptName = n["ScriptName"].as<std::string>("");
                 sc.active = n["Active"].as<bool>(true);
+                if (const YAML::Node items = n["Items"]) {
+                    for (const auto& it : items) {
+                        ECS::ScriptComponent::Item item;
+                        item.name = it["Name"].as<std::string>("");
+                        item.active = it["Active"].as<bool>(true);
+                        sc.items.push_back(std::move(item));
+                    }
+                } else {
+                    // 旧格式：Script: {ScriptName: ..., Active: ...}
+                    ECS::ScriptComponent::Item item;
+                    item.name = n["ScriptName"].as<std::string>("");
+                    if (!item.name.empty()) {
+                        sc.items.push_back(std::move(item));
+                    }
+                }
             }
         }