fix(i18n): hardkodierte Strings in Cluster/Users/Backups/Alerts bereinigen

- Cluster: statusTag() bekommt t-Parameter; Status-Labels (online/offline/
  joining/leaving/unknown) → cluster.status.* Keys
- Users: 'You'-Tag → t('users.you') / de: 'Ich'
- Backups: 'OK'-Status-Tag → t('backups.okTag')
- Alerts: Kanal-Kind-Labels + alle SMTP-Formular-Labels in t() überführt
- en/de: cluster.status.*, users.you, backups.okTag, alerts.smtp.*,
  alerts.kindWebhook/kindEmail ergänzt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

management-ui/src/pages/Backups/History.tsx

@@ -187,7 +187,7 @@ export default function HistoryTab() {
       title: t('backups.col.status'), dataIndex: 'status', width: 110,
       render: (s: Backup['status'], row) =>
         s === 'success'
-          ? <Tag color="green">OK</Tag>
+          ? <Tag color="green">{t('backups.okTag')}</Tag>
           : (
             <Tooltip title={row.error}>
               <Tag color="red">{t('backups.failedTag')}</Tag>