i18n: localize sidebar theme toggle, xray-status badge, and nodes menu

The sidebar theme submenu (Theme / Dark / Ultra dark) and the dashboard's
Xray status badge ("Xray is running" etc.) were hardcoded English strings.
Wire them through vue-i18n: ThemeSwitch.vue uses menu.theme/dark/ultraDark,
and XrayStatusCard.vue derives the badge text from the existing
pages.index.xrayStatus{Running,Stop,Error,Unknown} keys (status.js no
longer carries an English stateMsg field).

The "Nodes" menu item was already keyed as menu.nodes but only en-US and
fa-IR had a translation; add it to the other 11 languages, matching the
wording each file already uses for pages.nodes.title.
#4201

frontend/src/components/ThemeSwitch.vue

@@ -1,8 +1,11 @@
 <script setup>
 import { computed } from 'vue';
+import { useI18n } from 'vue-i18n';
 import { BulbFilled, BulbOutlined } from '@ant-design/icons-vue';
 import { theme, currentTheme, toggleTheme, toggleUltra, pauseAnimationsUntilLeave } from '@/composables/useTheme.js';
 
+const { t } = useI18n();
+
 const BulbIcon = computed(() => (theme.isDark ? BulbFilled : BulbOutlined));
 
 function onDarkChange() {
@@ -22,17 +25,17 @@ function onUltraClick() {
       <template #title>
         <span>
           <component :is="BulbIcon" />
-          <span class="theme-label">Theme</span>
+          <span class="theme-label">{{ t('menu.theme') }}</span>
         </span>
       </template>
 
       <a-menu-item id="change-theme" class="ant-menu-theme-switch">
-        <span>Dark</span>
+        <span>{{ t('menu.dark') }}</span>
         <a-switch :style="{ marginLeft: '2px' }" size="small" :checked="theme.isDark" @change="onDarkChange" />
       </a-menu-item>
 
       <a-menu-item v-if="theme.isDark" id="change-theme-ultra" class="ant-menu-theme-switch">
-        <span>Ultra dark</span>
+        <span>{{ t('menu.ultraDark') }}</span>
         <a-checkbox :style="{ marginLeft: '2px' }" :checked="theme.isUltra" @click="onUltraClick" />
       </a-menu-item>
     </a-sub-menu>