fix(web): 后端不可用统一用 BackendDownNotice 替代 404/手搓提示

apps/web/app/projects/[id]/toolbox/page.tsx

@@ -1,5 +1,4 @@
-import { notFound } from "next/navigation";
-
+import { BackendDownNotice } from "@/components/BackendDownNotice";
 import { ToolboxPage } from "@/components/toolbox/ToolboxPage";
 import { fetchProject, fetchToolbox } from "@/lib/api/server";
 
@@ -29,6 +28,6 @@ export default async function ToolboxRoutePage({
       />
     );
   } catch {
-    notFound();
+    return <BackendDownNotice className="m-6" />;
   }
 }