feat(frontend): 控制台 next-intl 中英双语

接入无 URL 前缀的 zh-CN/en，顶栏与外观设置可切换语言；选择写入 cookie 后刷新生效。

frontend/app/(main)/admin/demo/tabs/dashboard-tab.tsx

@@ -4,11 +4,13 @@
 'use client';
 
 import * as React from 'react';
+import { useTranslations } from 'next-intl';
 import { Code, Cpu, Database, HardDrive } from 'lucide-react';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
 import { Progress } from '@/components/ui/progress';
 
 export function DashboardTab() {
+  const t = useTranslations('admin.demo.dashboard');
   return (
     <div className='space-y-6'>
       <div className='grid grid-cols-1 md:grid-cols-3 gap-4'>
@@ -16,7 +18,7 @@ export function DashboardTab() {
         <Card className='border-dashed shadow-none'>
           <CardHeader className='flex flex-row items-center justify-between pb-2'>
             <span className='text-xs font-medium text-muted-foreground'>
-              容器 CPU 使用率
+              {t('cpuUsage')}
             </span>
             <Cpu className='size-4 text-primary' />
           </CardHeader>
@@ -25,7 +27,7 @@ export function DashboardTab() {
             <Progress value={42.8} className='h-1.5' />
             <p className='text-[10px] text-muted-foreground flex items-center gap-1'>
               <span className='size-1.5 rounded-full bg-emerald-500 inline-block animate-pulse' />
-              容器运行正常，负载平稳
+              {t('cpuStatus')}
             </p>
           </CardContent>
         </Card>
@@ -34,7 +36,7 @@ export function DashboardTab() {
         <Card className='border-dashed shadow-none'>
           <CardHeader className='flex flex-row items-center justify-between pb-2'>
             <span className='text-xs font-medium text-muted-foreground'>
-              存储已用容量
+              {t('storageUsage')}
             </span>
             <HardDrive className='size-4 text-primary' />
           </CardHeader>
@@ -45,7 +47,7 @@ export function DashboardTab() {
             </div>
             <Progress value={72.4} className='h-1.5' />
             <p className='text-[10px] text-muted-foreground'>
-              数据已同步远端 S3 存储桶，支持自动过期
+              {t('storageStatus')}
             </p>
           </CardContent>
         </Card>
@@ -54,7 +56,7 @@ export function DashboardTab() {
         <Card className='border-dashed shadow-none'>
           <CardHeader className='flex flex-row items-center justify-between pb-2'>
             <span className='text-xs font-medium text-muted-foreground'>
-              物理数据库
+              {t('database')}
             </span>
             <Database className='size-4 text-primary' />
           </CardHeader>
@@ -67,16 +69,16 @@ export function DashboardTab() {
             </div>
             <div className='flex items-center gap-3 text-xs text-muted-foreground'>
               <div>
-                活跃连接:{' '}
+                {t('activeConnections')}{' '}
                 <span className='font-semibold text-foreground'>12</span>
               </div>
               <div>
-                总表数量:{' '}
+                {t('totalTables')}{' '}
                 <span className='font-semibold text-foreground'>34</span>
               </div>
             </div>
             <p className='text-[10px] text-muted-foreground'>
-              链接池自动维护中，最大连接限制为 100
+              {t('dbStatus')}
             </p>
           </CardContent>
         </Card>
@@ -87,45 +89,45 @@ export function DashboardTab() {
         <CardHeader className='pb-3'>
           <CardTitle className='text-sm font-semibold flex items-center gap-1.5'>
             <Code className='size-4 text-primary' />
-            指标卡片 & 仪表盘设计规范
+            {t('dashboardDesignSpec')}
           </CardTitle>
         </CardHeader>
         <CardContent className='space-y-4'>
           <ul className='list-disc pl-4 text-xs text-muted-foreground space-y-1.5'>
             <li>
-              指标卡片统一采用{' '}
+              {t('spec.dashedBorder')}
               <code className='bg-muted px-1 py-0.5 rounded font-mono'>
                 border-dashed shadow-none
               </code>{' '}
-              作为边框和投影。
+              {t('spec.dashedBorder2')}
             </li>
             <li>
-              头部使用{' '}
+              {t('spec.headerLayout')}
               <code className='bg-muted px-1 py-0.5 rounded font-mono'>
                 flex flex-row items-center justify-between pb-2
               </code>{' '}
-              布局，左侧为标题小字，右侧为直接呈现的 Lucide 图标。
+              {t('spec.headerLayout2')}
             </li>
             <li>
-              数值强调使用且仅使用{' '}
+              {t('spec.valueStyle')}
               <code className='bg-muted px-1 py-0.5 rounded font-mono'>
                 text-2xl font-semibold tracking-tight
               </code>{' '}
-              展示。
+              {t('spec.valueStyle2')}
             </li>
             <li>
-              进度条使用{' '}
+              {t('spec.progressBar')}
               <code className='bg-muted px-1 py-0.5 rounded font-mono'>
                 h-1.5
               </code>{' '}
-              细条高度，不喧宾夺主。
+              {t('spec.progressBar2')}
             </li>
             <li>
-              底部的次要说明信息必须统一使用{' '}
+              {t('spec.secondaryText')}
               <code className='bg-muted px-1 py-0.5 rounded font-mono'>
                 text-[10px] text-muted-foreground
               </code>{' '}
-              等辅助类。
+              {t('spec.secondaryText2')}
             </li>
           </ul>
           <pre className='text-[11px] font-mono text-muted-foreground overflow-x-auto p-3 bg-background rounded border border-border/40 leading-relaxed'>