fix(frontend): 修复静态导出下切换语言无效的问题

frontend/components/providers/intl-provider.tsx

@@ -1,9 +1,18 @@
 'use client';
 
+import { useEffect, useState } from 'react';
 import { NextIntlClientProvider } from 'next-intl';
 import type { AbstractIntlMessages } from 'next-intl';
 import type { ReactNode } from 'react';
+import { resolveClientLocale } from '@/i18n/client';
 import type { AppLocale } from '@/i18n/config';
+import enMessages from '@/messages/en.json';
+import zhCNMessages from '@/messages/zh-CN.json';
+
+const messagesByLocale: Record<AppLocale, AbstractIntlMessages> = {
+  'zh-CN': zhCNMessages,
+  en: enMessages,
+};
 
 type Props = {
   locale: AppLocale;
@@ -11,14 +20,36 @@ type Props = {
   children: ReactNode;
 };
 
-export function AppIntlProvider({ locale, messages, children }: Props) {
+export function AppIntlProvider({
+  locale: ssrLocale,
+  messages: ssrMessages,
+  children,
+}: Props) {
+  // Static export (NEXT_STANDALONE_EXPORT) pre-renders every page at build time
+  // with the default locale, so the SSR locale is stale at runtime. Re-resolve
+  // from the NEXT_LOCALE cookie / browser language on the client. The first
+  // render stays identical to SSR to avoid a hydration mismatch, then flips —
+  // the brief flash matches the theme-hydration pattern (suppressHydrationWarning
+  // is already set on <html>/<body>).
+  const [clientLocale, setClientLocale] = useState<AppLocale | null>(null);
+
+  useEffect(() => {
+    const resolved = resolveClientLocale();
+    if (resolved !== ssrLocale) {
+      setClientLocale(resolved);
+      document.documentElement.lang = resolved;
+    }
+  }, [ssrLocale]);
+
+  const locale = clientLocale ?? ssrLocale;
+
   return (
     <NextIntlClientProvider
       locale={locale}
-      messages={messages}
+      messages={clientLocale ? messagesByLocale[clientLocale] : ssrMessages}
       timeZone='Asia/Shanghai'
     >
       {children}
     </NextIntlClientProvider>
   );
-}
+}