fix: API 500 错误返回具体原因，便于线上排查

src/lib/api.ts

@@ -56,8 +56,9 @@ export function apiHandler(handler: RouteHandler): RouteHandler {
           { status: 409 },
         );
       }
+      const detail = e instanceof Error ? `${e.name}: ${e.message}` : String(e);
       console.error(`[API ${req.method} ${req.nextUrl.pathname}]`, e);
-      return NextResponse.json({ error: "操作失败" }, { status: 500 });
+      return NextResponse.json({ error: `操作失败 [${detail}]` }, { status: 500 });
     }
   };
 }