refactor(i18n): 移除多语言支持及相关组件，切换登录页文本为中文

- 删除英文和中文语言文件，去除国际化配置
- 移除语言切换组件 LangSwitch.vue
- 登录页中静态替换多语言文本为中文文本
- 站点头部登录、退出等文案替换为中文
- 更新 Nuxt 配置，移除 i18n 模块和相关配置
- 保持核心功能不变，只保留中文语言显示

app/components/LangSwitch.vue

@@ -1,53 +0,0 @@
-<template>
-  <a-dropdown :trigger="['click']" placement="bottomRight">
-    <a-button type="text" class="lang-btn">
-      <template #icon>
-        <GlobalOutlined />
-      </template>
-      <span class="current-lang">{{ currentLocaleName }}</span>
-      <DownOutlined class="ml-1" />
-    </a-button>
-    <template #overlay>
-      <a-menu @click="switchLocale">
-        <a-menu-item v-for="loc in availableLocales" :key="loc.code">
-          <div class="flex items-center justify-between gap-4">
-            <span>{{ loc.name }}</span>
-            <CheckOutlined v-if="loc.code === currentLocale" class="text-green-500" />
-          </div>
-        </a-menu-item>
-      </a-menu>
-    </template>
-  </a-dropdown>
-</template>
-
-<script setup lang="ts">
-import { GlobalOutlined, DownOutlined, CheckOutlined } from '@ant-design/icons-vue'
-
-const { locale: currentLocale, locales, setLocale } = useI18n()
-
-const availableLocales = computed(() => {
-  return (locales.value as Array<{ code: string; name: string }>).map((l) => ({
-    code: l.code,
-    name: l.name
-  }))
-})
-
-const currentLocaleName = computed(() => {
-  const found = availableLocales.value.find((l) => l.code === currentLocale.value)
-  return found?.name || currentLocale.value
-})
-
-async function switchLocale({ key }: { key: string }) {
-  await setLocale(key)
-}
-</script>
-
-<style scoped>
-.lang-btn {
-  @apply text-gray-300 hover:text-white;
-}
-
-.current-lang {
-  @apply text-sm;
-}
-</style>

app/components/SiteHeader.vue

@@ -44,7 +44,7 @@
           <!-- PC 端：登录/头像 -->
           <div class="hidden md:flex items-center gap-3">
             <template v-if="!isAuthed">
-              <a-button type="primary" @click="navigateTo('/login')">{{ $t('nav.login') }}</a-button>
+              <a-button type="primary" @click="navigateTo('/login')">{{ '登录' }}</a-button>
             </template>
             <template v-else>
               <!-- 用户头像 -->
@@ -66,7 +66,7 @@
                       <a-menu-item key="admin">⚙️ 后台管理</a-menu-item>
                     </template>
                     <a-menu-divider />
-                    <a-menu-item key="logout">{{ $t('nav.logout') }}</a-menu-item>
+                    <a-menu-item key="logout">{{ '退出登录' }}</a-menu-item>
                   </a-menu>
                 </template>
               </a-dropdown>
@@ -84,7 +84,7 @@
     </a-layout-header>
   </a-affix>
 
-  <a-drawer v-model:open="open" :title="$t('nav.navigation') || '导航'" placement="right">
+  <a-drawer v-model:open="open" :title="'导航' || '导航'" placement="right">
     <a-menu mode="inline" :selected-keys="selectedKeys">
       <template v-for="item in nav" :key="item.key">
         <a-sub-menu v-if="item.children && item.children.length" :key="item.key">
@@ -103,11 +103,11 @@
       </template>
     </a-menu>
     <div class="mt-4">
-      <a-button v-if="!isAuthed" block type="primary" @click="onNav('/login')">{{ $t('nav.login') || '登录' }}</a-button>
+      <a-button v-if="!isAuthed" block type="primary" @click="onNav('/login')">{{ '登录' || '登录' }}</a-button>
       <template v-else>
         <a-button block type="primary" class="mb-2" @click="onNav('/profile')">个人中心</a-button>
         <a-button v-if="isSuperAdmin" block @click="onNav('/admin')">⚙️ 后台管理</a-button>
-        <a-button block danger class="mt-2" @click="logout">{{ $t('nav.logout') || '退出登录' }}</a-button>
+        <a-button block danger class="mt-2" @click="logout">{{ '退出登录' || '退出登录' }}</a-button>
       </template>
     </div>
   </a-drawer>