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/AppLayout.tsx

@@ -14,7 +14,7 @@ const PAGE_TITLES: Record<string, string> = {
   '/dashboard':     'nav.dashboard',
   '/domains':       'nav.domains',
   '/backends':      'nav.backends',
-  '/routing-rules': 'nav.routing',
+  '/routing-rules':  'nav.routing',
   '/networks':      'nav.networks',
   '/ip-addresses':  'nav.ipAddresses',
   '/firewall/live': 'nav.firewallLive',