修复: 设置页渲染崩溃(AppearanceSection 静态 import @/i18n 触发 TDZ)

- AppearanceSection 去掉 import i18n from '@/i18n',改用 useI18n() 获取 locale
- 根因:@/i18n 模块顶层调 useAppSettingsStore().get(),打包后初始化顺序冲突
- 这是设置页 + AI 独立窗口反复报 Cannot access 'u' before initialization 的根因

src/components/settings/AppearanceSection.vue

@@ -43,8 +43,8 @@
 
 <script setup lang="ts">
 import { reactive, watch, onMounted, useTemplateRef } from 'vue'
+import { useI18n } from 'vue-i18n'
 import { useAppSettingsStore } from '@/stores/appSettings'
-import i18n from '@/i18n'
 import SettingRow from './SettingRow.vue'
 
 // ============================================================
@@ -53,6 +53,7 @@ import SettingRow from './SettingRow.vue'
 // 阶段5:SettingRow 封装行布局,控件变更后调 markSaved 显"已保存"
 // ============================================================
 const appSettings = useAppSettingsStore()
+const { locale } = useI18n()
 
 const settings = reactive({
   theme: appSettings.get<string>('df-theme', 'dark'),
@@ -107,7 +108,7 @@ watch(() => settings.streamingMd, (val) => {
 watch(() => settings.language, (val) => {
   void appSettings.set('df-language', val)
   // 同步 i18n 实例，让界面立即跟随语言切换
-  i18n.global.locale.value = val as 'zh-CN' | 'en'
+  locale.value = val as 'zh-CN' | 'en'
 })
 
 onMounted(() => {