feat(web): add Data page with embedded nofxos.ai dashboard

- Add Data navigation item before Market in header
- Create DataPage component with iframe embedding
- Publicly accessible without login required

web/src/pages/DataPage.tsx

@@ -0,0 +1,16 @@
+import { useLanguage } from '../contexts/LanguageContext'
+
+export function DataPage() {
+  const { language } = useLanguage()
+
+  return (
+    <div className="w-full h-[calc(100vh-64px)]">
+      <iframe
+        src="https://nofxos.ai/dashboard"
+        title={language === 'zh' ? '数据中心' : 'Data Center'}
+        className="w-full h-full border-0"
+        allow="fullscreen"
+      />
+    </div>
+  )
+}