i18n(frontend): translate every remaining English string on the index page

Closes the index page's i18n coverage. Combined with the page-chrome
commit, every label users see on the dashboard is now sourced from
the TOML translation files.

Per file:
- IndexPage.vue: loading-spinner tip (initial + dynamic).
- BackupModal.vue: modal title, both list-item titles + descriptions
  ("Back up" / "Restore"), in-flight busy tips ("Importing database…"
  / "Restarting panel…").
- PanelUpdateModal.vue: modal title, update-available alert,
  current/latest version row labels, "Up to date" tag + label,
  primary action button. Modal.confirm now uses the translated
  panelUpdateDialog / panelUpdateDialogDesc with #version#
  substitution; success toast uses panelUpdateStartedPopover.
- LogModal.vue: title slot ("Logs"). The Debug/Info/Notice/Warning/
  Error log-level options stay literal — they're xray's wire values,
  not user-facing labels (matches the existing settings-page choice).
- XrayLogModal.vue: title + Filter label. Direct/Blocked/Proxy stay
  literal for the same reason.
- VersionModal.vue: modal title + xray-switch alert + per-file
  tooltip + "Update all" button + custom-geo collapse header. The
  Modal.confirm flows for switchXrayVersion + updateGeofile use
  translated dialog/desc with #version# / #filename# substitution.
- CpuHistoryModal.vue: title slot.
- CustomGeoSection.vue: routing-hint alert, Add / Update-all buttons,
  every column title (computed for live locale), copy/edit/download/
  delete tooltips, copy toast, delete-confirm modal, empty-state
  text.
- CustomGeoFormModal.vue: add/edit titles, OK/cancel labels, Type/
  Alias/URL field labels, alias placeholder, all three validation
  toasts.

Total: ~50 strings localised across 8 index-page files. The Hello /
Welcome login headline cycle and a handful of literal xray wire
values (Direct/Blocked/Proxy/log levels) are intentionally kept
hardcoded.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/pages/index/BackupModal.vue

@@ -1,7 +1,10 @@
 <script setup>
+import { useI18n } from 'vue-i18n';
 import { DownloadOutlined, UploadOutlined } from '@ant-design/icons-vue';
 import { HttpUtil, PromiseUtil } from '@/utils';
 
+const { t } = useI18n();
+
 defineProps({
   open: { type: Boolean, default: false },
   basePath: { type: String, default: '' },
@@ -32,7 +35,7 @@ function importDb() {
     formData.append('db', dbFile);
 
     close();
-    emit('busy', { busy: true, tip: 'Importing database…' });
+    emit('busy', { busy: true, tip: t('pages.index.importDatabase') + '…' });
 
     const upload = await HttpUtil.post('/panel/api/server/importDB', formData, {
       headers: { 'Content-Type': 'multipart/form-data' },
@@ -42,7 +45,7 @@ function importDb() {
       return;
     }
 
-    emit('busy', { busy: true, tip: 'Restarting panel…' });
+    emit('busy', { busy: true, tip: t('pages.settings.restartPanel') + '…' });
     const restart = await HttpUtil.post('/panel/setting/restartPanel');
     if (restart?.success) {
       await PromiseUtil.sleep(5000);
@@ -56,12 +59,12 @@ function importDb() {
 </script>
 
 <template>
-  <a-modal :open="open" title="Database backup & restore" :closable="true" :footer="null" @cancel="close">
+  <a-modal :open="open" :title="t('pages.index.backupTitle')" :closable="true" :footer="null" @cancel="close">
     <a-list bordered class="backup-list">
       <a-list-item class="backup-item">
         <a-list-item-meta>
-          <template #title>Back up</template>
-          <template #description>Click to download a .db file containing a backup of your current database to your device.</template>
+          <template #title>{{ t('pages.index.exportDatabase') }}</template>
+          <template #description>{{ t('pages.index.exportDatabaseDesc') }}</template>
         </a-list-item-meta>
         <a-button type="primary" @click="exportDb">
           <template #icon><DownloadOutlined /></template>
@@ -70,8 +73,8 @@ function importDb() {
 
       <a-list-item class="backup-item">
         <a-list-item-meta>
-          <template #title>Restore</template>
-          <template #description>Click to upload a .db file. The panel restarts after restore — your session will reconnect automatically.</template>
+          <template #title>{{ t('pages.index.importDatabase') }}</template>
+          <template #description>{{ t('pages.index.importDatabaseDesc') }}</template>
         </a-list-item-meta>
         <a-button type="primary" @click="importDb">
           <template #icon><UploadOutlined /></template>