feat(frontend): add next-intl bilingual i18n for core paths

Wire next-intl without locale routes, add zh-CN/en catalogs, language
switcher, and migrate layout/auth/settings UI copy. Document i18n rules
in AGENTS.md and keep static export builds working.

frontend/app/(main)/settings/page.tsx

@@ -1,6 +1,7 @@
 'use client';
 
 import Link from 'next/link';
+import { useTranslations } from 'next-intl';
 import {
   Card,
   CardContent,
@@ -9,39 +10,40 @@ import {
 } from '@/components/ui/card';
 import { Bell, Key, Palette, UserRound } from 'lucide-react';
 
-/* 设置项 */
-const settingsItems = [
-  {
-    title: '个人资料',
-    description: '查看您的账户信息',
-    icon: UserRound,
-    href: '/settings/profile',
-    category: '个人设置',
-  },
-  {
-    title: '访问令牌 (AccessToken)',
-    description: '管理用于 API 访问的个人 Token',
-    icon: Key,
-    href: '/settings/access-token',
-    category: '个人设置',
-  },
-  {
-    title: '通知设置',
-    description: '设置您的通知偏好',
-    icon: Bell,
-    href: '/settings/notifications',
-    category: '账户设置',
-  },
-  {
-    title: '外观设置',
-    description: '自定义界面主题 and 显示',
-    icon: Palette,
-    href: '/settings/appearance',
-    category: '个人设置',
-  },
-];
-
 export default function SettingsPage() {
+  const t = useTranslations('settings');
+
+  const settingsItems = [
+    {
+      title: t('items.profile'),
+      description: t('items.profileDesc'),
+      icon: UserRound,
+      href: '/settings/profile',
+      category: t('categories.personal'),
+    },
+    {
+      title: t('items.accessToken'),
+      description: t('items.accessTokenDesc'),
+      icon: Key,
+      href: '/settings/access-token',
+      category: t('categories.personal'),
+    },
+    {
+      title: t('items.notifications'),
+      description: t('items.notificationsDesc'),
+      icon: Bell,
+      href: '/settings/notifications',
+      category: t('categories.account'),
+    },
+    {
+      title: t('items.appearance'),
+      description: t('items.appearanceDesc'),
+      icon: Palette,
+      href: '/settings/appearance',
+      category: t('categories.personal'),
+    },
+  ];
+
   const groupedSettings = settingsItems.reduce(
     (acc, item) => {
       if (!acc[item.category]) {
@@ -55,7 +57,7 @@ export default function SettingsPage() {
 
   return (
     <div className='space-y-6 py-6'>
-      <div className='font-semibold text-lg'>设置</div>
+      <div className='font-semibold text-lg'>{t('title')}</div>
 
       {Object.entries(groupedSettings).map(([category, items]) => (
         <div key={category} className='space-y-4'>

frontend/app/layout.tsx

@@ -1,5 +1,6 @@
 import type { Metadata } from 'next';
 import { Inter } from 'next/font/google';
+import { getLocale, getMessages, getTranslations } from 'next-intl/server';
 import { Toaster } from '@/components/ui/sonner';
 import { ThemeProvider } from '@/components/layout/theme-provider';
 import { CustomThemeProvider } from '@/lib/theme';
@@ -7,8 +8,10 @@ import { BellRingProvider } from '@/contexts/bell-ring-context';
 import { NotificationSettingsProvider } from '@/contexts/notification-settings-context';
 import { UserProvider } from '@/contexts/user-context';
 import { AppQueryProvider } from '@/components/providers/query-provider';
+import { AppIntlProvider } from '@/components/providers/intl-provider';
 import { SiteTitleUpdater } from '@/components/providers/title-updater';
 import { RobotsMeta } from '@/components/layout/robots-meta';
+import type { AppLocale } from '@/i18n/config';
 import './globals.css';
 
 const inter = Inter({
@@ -17,19 +20,25 @@ const inter = Inter({
   display: 'swap',
 });
 
-export const metadata: Metadata = {
-  title: 'Wavelet Platform',
-  description: '通用二次开发标准范式平台',
-};
+export async function generateMetadata(): Promise<Metadata> {
+  const t = await getTranslations('metadata');
+  return {
+    title: t('title'),
+    description: t('description'),
+  };
+}
 
-export default function RootLayout({
+export default async function RootLayout({
   children,
 }: Readonly<{
   children: React.ReactNode;
 }>) {
+  const locale = (await getLocale()) as AppLocale;
+  const messages = await getMessages();
+
   return (
     <html
-      lang='zh-CN'
+      lang={locale}
       className={`hide-scrollbar font-sans ${inter.variable}`}
       suppressHydrationWarning
     >
@@ -42,16 +51,18 @@ export default function RootLayout({
         >
           <CustomThemeProvider>
             <AppQueryProvider>
-              <SiteTitleUpdater />
-              <RobotsMeta />
-              <UserProvider>
-                <NotificationSettingsProvider>
-                  <BellRingProvider>
-                    {children}
-                    <Toaster position='top-center' />
-                  </BellRingProvider>
-                </NotificationSettingsProvider>
-              </UserProvider>
+              <AppIntlProvider locale={locale} messages={messages}>
+                <SiteTitleUpdater />
+                <RobotsMeta />
+                <UserProvider>
+                  <NotificationSettingsProvider>
+                    <BellRingProvider>
+                      {children}
+                      <Toaster position='top-center' />
+                    </BellRingProvider>
+                  </NotificationSettingsProvider>
+                </UserProvider>
+              </AppIntlProvider>
             </AppQueryProvider>
           </CustomThemeProvider>
         </ThemeProvider>