feat: add language selector and lazy-load i18n infrastructure

Updated i18n.ts with SUPPORTED_LOCALES, setLocale() lazy loading,
localStorage persistence. Added language selector in Settings.vue.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/views/Settings.vue

@@ -453,6 +453,23 @@
       </div>
     </div>
 
+    <!-- Language Section -->
+    <div class="glass-card px-6 py-6 mb-6">
+      <h2 class="text-xl font-semibold text-white/96 mb-2">Language</h2>
+      <p class="text-sm text-white/60 mb-4">Choose your preferred language</p>
+      <div class="flex gap-3 flex-wrap">
+        <button
+          v-for="loc in supportedLocales"
+          :key="loc.code"
+          @click="changeLocale(loc.code)"
+          class="glass-button px-4 py-2 rounded-lg text-sm font-medium transition-all"
+          :class="currentLocale === loc.code ? 'ring-2 ring-orange-400/60 bg-white/10' : ''"
+        >
+          <span class="mr-2">{{ loc.flag }}</span>{{ loc.name }}
+        </button>
+      </div>
+    </div>
+
     <!-- Claude Authentication Section -->
     <div class="glass-card px-6 py-6 mb-6">
       <h2 class="text-xl font-semibold text-white/96 mb-2">{{ t('settings.claudeAuth') }}</h2>
@@ -818,6 +835,7 @@
 import { computed, ref, onMounted, nextTick } from 'vue'
 import { useRouter } from 'vue-router'
 import { useI18n } from 'vue-i18n'
+import { SUPPORTED_LOCALES, setLocale, type SupportedLocale } from '@/i18n'
 import { useAppStore } from '../stores/app'
 import { useUIModeStore } from '@/stores/uiMode'
 import { useAIPermissionsStore, AI_PERMISSION_CATEGORIES } from '@/stores/aiPermissions'
@@ -827,8 +845,13 @@ import { useModalKeyboard } from '@/composables/useModalKeyboard'
 import type { UIMode } from '@/types/api'
 
 const router = useRouter()
-const { t } = useI18n()
+const { t, locale } = useI18n()
 const store = useAppStore()
+const supportedLocales = SUPPORTED_LOCALES
+const currentLocale = computed(() => locale.value)
+async function changeLocale(code: string) {
+  await setLocale(code as SupportedLocale)
+}
 const uiMode = useUIModeStore()
 const aiPermissions = useAIPermissionsStore()
 const aiCategoryGroups = computed(() => {