feat: 前端 Error Boundary + 体验改进

- 新增 ErrorBoundary 组件: 捕获组件崩溃,显示友好错误页+重试按钮
- App: 用 ErrorBoundary 包裹,标题改为「先知 Profeto」
- Matches 页面:
  - 预测模式切换 (单次/多 Agent)
  - 加载中动画指示
  - 预测中状态提示
  - 错误提示可关闭

frontend/src/App.tsx

@@ -1,15 +1,18 @@
+import { ErrorBoundary } from './components/ErrorBoundary'
 import Matches from './pages/Matches'
 
 export default function App() {
   return (
-    <div className="min-h-screen bg-gray-50">
-      <header className="bg-white border-b px-6 py-3 flex items-center justify-between">
-        <h1 className="text-xl font-bold text-blue-700">⚽ Profeto</h1>
-        <span className="text-sm text-gray-500">足球 LLM 预测服务</span>
-      </header>
-      <main className="max-w-5xl mx-auto p-6">
-        <Matches />
-      </main>
-    </div>
+    <ErrorBoundary>
+      <div className="min-h-screen bg-gray-50">
+        <header className="bg-white border-b px-6 py-3 flex items-center justify-between">
+          <h1 className="text-xl font-bold text-blue-700">⚽ 先知 Profeto</h1>
+          <span className="text-sm text-gray-500">足球 LLM 预测服务</span>
+        </header>
+        <main className="max-w-5xl mx-auto p-6">
+          <Matches />
+        </main>
+      </div>
+    </ErrorBoundary>
   )
 }