feat(label-studio): 添加预加载组件以优化加载性能

- 实现 LabelStudioPreloader 组件用于预加载资源
- 使用 iframe 在后台加载 /lsf/lsf.html 页面
- 设置 2 秒延迟避免与初始页面加载竞争资源
- 配置隐藏样式确保预加载过程不可见
- 添加清理函数防止内存泄漏
- 实现条件渲染控制预加载时机

frontend/src/components/business/LabelStudioPreloader.tsx

@@ -0,0 +1,35 @@
+import { useEffect, useState } from "react";
+
+const PRELOAD_URL = "/lsf/lsf.html";
+
+export default function LabelStudioPreloader() {
+  const [shouldLoad, setShouldLoad] = useState(false);
+
+  useEffect(() => {
+    // Delay preloading slightly to avoid contending with initial page load resources
+    // Using 2000ms (2 seconds) as a reasonable idle time approximation
+    const timer = setTimeout(() => {
+      setShouldLoad(true);
+    }, 2000);
+
+    return () => clearTimeout(timer);
+  }, []);
+
+  if (!shouldLoad) return null;
+
+  return (
+    <iframe
+      src={PRELOAD_URL}
+      style={{
+        display: "none",
+        width: 0,
+        height: 0,
+        border: 0,
+        position: "absolute",
+        visibility: "hidden"
+      }}
+      title="Label Studio Preloader"
+      aria-hidden="true"
+    />
+  );
+}