fix(studio): 笔记切换页面不刷新 + 侧边栏错误提示友好化

- WorkspaceRoutes 给 StudioNotebookDetailPage 加 key={notebookId}，切换笔记时强制重新挂载
- createSearchSpace 接口失败时解析响应体 detail 字段，直接展示服务端错误信息

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend-web/src/components/workspace/workspace-nav-studio.tsx

@@ -34,8 +34,6 @@ const NAV_ITEM_CLASS =
   "data-[active=true]:bg-primary/15 data-[active=true]:text-primary data-[active=true]:shadow-none " +
   "dark:hover:bg-primary/15 dark:data-[active=true]:bg-primary/25 dark:data-[active=true]:text-primary-foreground";
 
-const SIDEBAR_PREVIEW_COUNT = 5;
-
 export function WorkspaceNavStudio() {
   const { notebooks, isLoading, isError } = useStudioNotebooks();
   const { pathname } = useLocation();
@@ -71,6 +69,7 @@ export function WorkspaceNavStudio() {
     return null;
   }
 
+  const SIDEBAR_PREVIEW_COUNT = 2;
   const preview = notebooks.slice(0, SIDEBAR_PREVIEW_COUNT);
 
   return (