fix: workspace_tree id=__root__ returns children

wwwroot/api/workspace_tree.dspy

@@ -29,13 +29,12 @@ async with DBPools().sqlorContext(dbname) as sor:
             ws_dir = ws if ws.startswith('/') else workspace_base + '/' + org_id + '/' + pname
 
 if not ws_dir or not os.path.isdir(ws_dir):
-    if not node_id or node_id == '__root__':
+    if not node_id:
         return [{"id": "__root__", "parentid": "", "label": "📁 工作空间（不可用）", "path": "", "is_leaf": False}]
     return []
 
-# 确定要扫描的目录
-if not node_id or node_id == '__root__':
-    # 初始加载：返回根节点
+# 初始加载：无 id 参数，只返回根节点
+if not node_id:
     return [{
         "id": "__root__",
         "parentid": "",