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/ActionButtons.tsx

@@ -1,6 +1,7 @@
 import { Button, Popconfirm, Space, Tooltip } from 'antd'
 import { DeleteOutlined, EditOutlined } from '@ant-design/icons'
 import { useTranslation } from 'react-i18next'
+import { useAuthStore } from '../stores/auth'
 
 // ActionButtons is the standard "Edit / Delete" pair used at the
 // end of every CRUD table row. Centralising it means we only style
@@ -8,6 +9,9 @@ import { useTranslation } from 'react-i18next'
 //
 // Either prop may be omitted to suppress that button — useful for
 // rows that aren't editable (e.g. builtin services).
+// Viewer-role accounts automatically get delete disabled — mutations
+// are blocked at the API level too, but hiding the button avoids
+// confusing "access denied" errors for read-only users.
 interface ActionButtonsProps {
   onEdit?: () => void
   onDelete?: () => void
@@ -28,6 +32,14 @@ export default function ActionButtons({
   editDisabledReason, deleteDisabledReason,
 }: ActionButtonsProps) {
   const { t } = useTranslation()
+  const role = useAuthStore((s) => s.user?.role)
+  const isViewer = role === 'viewer'
+
+  const delDisabled = deleteDisabled || isViewer
+  const delDisabledReason = isViewer
+    ? t('auth.viewerBadge')
+    : deleteDisabledReason
+
   return (
     <Space size={4}>
       {onEdit && (
@@ -42,8 +54,8 @@ export default function ActionButtons({
         </Tooltip>
       )}
       {onDelete && (
-        deleteDisabled ? (
-          <Tooltip title={deleteDisabledReason ?? t('common.delete')}>
+        delDisabled ? (
+          <Tooltip title={delDisabledReason ?? t('common.delete')}>
             <Button type="text" size="small" danger icon={<DeleteOutlined />} disabled />
           </Tooltip>
         ) : (