feat(ui): (a) Backends + Routing-Rules + Settings pages + Sidebar

CRUD-Pages analog Domains:
* Backends: AntD Table + Modal-Form mit name, scheme, address, port,
  health_check_path, active. TanStack-Query gegen /api/v1/backends.
* RoutingRules: Table mit Domain-Name- und Backend-Label-Resolution,
  Modal mit Select-Pickern für Domain + Backend, Path-Prefix,
  Priority, Active. Drei parallele Queries (rules, domains, backends)
  liefern die Listen.
* Settings: read-only Descriptions-Cards mit /system/health und
  /setup/status. Editable Werte folgen später.

Sidebar erweitert um Backends, Routing-Rules, Settings (mit AntD-
Icons). i18n de/en für alle drei neuen Seiten.

bun run build + npx tsc -b strict (0 errors). Live-Smoke gegen API:
SPA-Routes /backends, /routing-rules, /settings antworten 200 mit
index.html (NoRoute fallback wirkt).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

management-ui/src/pages/Settings/index.tsx

@@ -0,0 +1,66 @@
+import { Card, Descriptions, Spin, Typography } from 'antd'
+import { useQuery } from '@tanstack/react-query'
+import { useTranslation } from 'react-i18next'
+
+import apiClient, { isEnvelope } from '../../api/client'
+
+interface SetupStatus {
+  completed: boolean
+  admin_email: string
+  fqdn: string
+}
+
+interface SystemHealth {
+  status: string
+  version: string
+}
+
+export default function SettingsPage() {
+  const { t } = useTranslation()
+
+  const { data: setupStatus, isLoading: loadingSetup } = useQuery({
+    queryKey: ['setup', 'status'],
+    queryFn: async () => {
+      const r = await apiClient.get('/setup/status')
+      if (isEnvelope(r.data)) return r.data.data as SetupStatus
+      return null
+    },
+  })
+
+  const { data: health, isLoading: loadingHealth } = useQuery({
+    queryKey: ['system', 'health'],
+    queryFn: async () => {
+      const r = await apiClient.get('/system/health')
+      if (isEnvelope(r.data)) return r.data.data as SystemHealth
+      return null
+    },
+  })
+
+  if (loadingSetup || loadingHealth) {
+    return <Spin />
+  }
+
+  return (
+    <div>
+      <Typography.Title level={3}>{t('settings.title')}</Typography.Title>
+      <Typography.Paragraph type="secondary">{t('settings.intro')}</Typography.Paragraph>
+
+      <Card title={t('settings.systemInfo')} style={{ marginBottom: 16 }}>
+        <Descriptions column={1}>
+          <Descriptions.Item label={t('settings.version')}>{health?.version ?? '—'}</Descriptions.Item>
+          <Descriptions.Item label={t('settings.status')}>{health?.status ?? '—'}</Descriptions.Item>
+        </Descriptions>
+      </Card>
+
+      <Card title={t('settings.setupInfo')}>
+        <Descriptions column={1}>
+          <Descriptions.Item label={t('settings.adminEmail')}>{setupStatus?.admin_email ?? '—'}</Descriptions.Item>
+          <Descriptions.Item label={t('settings.fqdn')}>{setupStatus?.fqdn ?? '—'}</Descriptions.Item>
+          <Descriptions.Item label={t('settings.setupCompleted')}>
+            {setupStatus?.completed ? t('common.yes') : t('common.no')}
+          </Descriptions.Item>
+        </Descriptions>
+      </Card>
+    </div>
+  )
+}