feat: workspace 目录树服务端懒加载

- api.ts: listWorkspaceDirectories 支持 parent_path 查询; WorkspaceDirectory 增加 has_children; 同步 WorkspaceBoundApi 签名
- AuthContext: 绑定透传 parentPath
- scriptWorkspaceStore: 新增 expandedPaths/loadingChildrenPaths/loadedChildPaths, loadChildren/toggleExpanded, 局部刷新 createFolder/deleteDirectory
- WorkspaceTree: 移除 useState, 改为受控展开/加载状态
- ScriptExplorer: 从 store 读取并透传展开状态与 toggle

frontend/app/services/api.ts

@@ -191,6 +191,7 @@ export type WorkspaceDirectory = {
   path: string;
   name: string;
   parent_path: string;
+  has_children?: boolean;
 };
 
 type ApiEnvelope<T> = {
@@ -443,9 +444,13 @@ export async function deleteScript(
 
 export async function listWorkspaceDirectories(
   workspaceId: string,
+  parentPath: string = "",
 ): Promise<WorkspaceDirectory[]> {
+  const query = parentPath
+    ? `?parent_path=${encodeURIComponent(parentPath)}`
+    : "";
   const data = await apiRequest<{ directories: WorkspaceDirectory[] }>(
-    "/api/v1/workspace-tree",
+    `/api/v1/workspace-directories${query}`,
     {},
     workspaceId,
   );
@@ -1325,9 +1330,9 @@ export type WorkspaceBoundApi = {
   setScriptLock: (
     scriptId: string,
     isLocked: boolean,
-  ) => Promise<ScriptItem>;
-  listWorkspaceDirectories: () => Promise<WorkspaceDirectory[]>;
-  createWorkspaceDirectory: (
+ ) => Promise<ScriptItem>;
+  listWorkspaceDirectories: (parentPath?: string) => Promise<WorkspaceDirectory[]>;
+ createWorkspaceDirectory: (
     directoryName: string,
     parentPath?: string,
   ) => Promise<WorkspaceDirectory>;