feat(ui): Quick-Toggles, Config-Preview, Dashboard-Alerts, Domain-Detail-Health

Quick-Toggle-Switches (kein Modal nötig) für: Backends, Backend-Server,
DNS-Zonen, DNS-Records, Domains (active), Firewall-Rules, NAT-Rules,
Forward-Proxy ACLs, Routing-Rules.

Dashboard: Alert-Banner für komplett ausgefallene Backends (HAProxy-Stats)
und Domains im Maintenance-Mode.

Domain-Detail: HAProxy-Live-Health-Badge (15s Polling), TLS-Cert
ausstellen/erneuern direkt aus dem Detail, Routing-Rules-Panel inline.

Config-Preview (Settings): alle 4 Generatoren (haproxy, nftables, squid,
unbound) rendern via RenderToString ohne Disk-Write — GET /system/config-preview.

ActionButtons: Viewer-Rolle blendet Delete aus (RBAC-Ergänzung).

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

management-ui/src/components/Layout/Sidebar.tsx

@@ -6,6 +6,7 @@ import apiClient, { isEnvelope } from '../../api/client'
 import {
   ApartmentOutlined,
   BellOutlined,
+  BranchesOutlined,
   ClockCircleOutlined,
   CloudServerOutlined,
   ClusterOutlined,
@@ -53,8 +54,9 @@ const NAV: NavSection[] = [
   {
     labelKey: 'nav.section.routing',
     items: [
-      { path: '/domains',  labelKey: 'nav.domains',  icon: <GlobalOutlined /> },
-      { path: '/backends', labelKey: 'nav.backends', icon: <DatabaseOutlined /> },
+      { path: '/domains',       labelKey: 'nav.domains',  icon: <GlobalOutlined /> },
+      { path: '/backends',      labelKey: 'nav.backends', icon: <DatabaseOutlined /> },
+      { path: '/routing-rules', labelKey: 'nav.routing',  icon: <BranchesOutlined /> },
     ],
   },
   {