fix(backends): Backend-Löschen verweigern wenn Routing-Regeln darauf zeigen (v1.1.142)

- Service: Pre-Check auf routing_rules.backend_id → ErrInUse vor DELETE
- Handler: ErrInUse → HTTP 409 Conflict statt 500 (response.Conflict helper)
- UI: Delete-Button deaktiviert + Tooltip "Von N Regeln verwendet" wenn Referenzen existieren

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

management-ui/src/i18n/locales/de/common.json

@@ -387,6 +387,7 @@
     "serverHintCreate": "Speichern legt nur den Pool an. Server kommen im nächsten Schritt — Pool öffnen → „Server hinzufügen\".",
     "actions": "Aktionen",
     "deleteConfirm": "Backend-Pool {{name}} wirklich löschen? Alle Server im Pool werden mitentfernt.",
+    "deleteInUse": "Von {{n}} Routing-Regel(n) verwendet — zuerst diese löschen",
     "backToList": "Zurück zur Übersicht",
     "settingsCard": "Pool-Einstellungen",
     "healthCheckHint": "HTTP-Pfad den HAProxy alle 5s pro Server prüft. Leer lassen = kein Health-Check.",

management-ui/src/i18n/locales/en/common.json

@@ -387,6 +387,7 @@
     "serverHintCreate": "Saving creates the pool only. Add servers in the next step — open the pool and click “Add server”.",
     "actions": "Actions",
     "deleteConfirm": "Really delete backend pool {{name}}? All servers in the pool will be removed too.",
+    "deleteInUse": "Used by {{n}} routing rule(s) — remove those first",
     "backToList": "Back to backends",
     "settingsCard": "Pool settings",
     "healthCheckHint": "HTTP path HAProxy probes every 5s per server. Leave empty to disable health checks.",

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

@@ -97,6 +97,15 @@ async function listDomains(): Promise<DomainFull[]> {
   return (r.data.data as { domains?: DomainFull[] }).domains ?? []
 }
 
+interface RoutingRule { id: number; backend_id: number }
+async function listRoutingRules(): Promise<RoutingRule[]> {
+  try {
+    const r = await apiClient.get('/routing-rules')
+    if (!isEnvelope(r.data)) return []
+    return (r.data.data as { routing_rules?: RoutingRule[] }).routing_rules ?? []
+  } catch { return [] }
+}
+
 interface HAProxyStat {
   backend: string; server: string; status: string
   sessions: number; bytes_in: number; bytes_out: number
@@ -124,6 +133,7 @@ export default function BackendsPage() {
 
   const { data, isLoading } = useQuery({ queryKey: ['backends'], queryFn: listBackends })
   const { data: domains } = useQuery({ queryKey: ['domains'], queryFn: listDomains })
+  const { data: routingRules } = useQuery({ queryKey: ['routing-rules'], queryFn: listRoutingRules })
   const { data: services } = useQuery({
     queryKey: ['system', 'services'],
     queryFn: async () => {
@@ -177,6 +187,9 @@ export default function BackendsPage() {
   const domainsForBackend = (id: number) =>
     (domains ?? []).filter(d => d.primary_backend_id === id)
 
+  const ruleCountForBackend = (id: number) =>
+    (routingRules ?? []).filter(r => r.backend_id === id).length
+
   const [creating, setCreating] = useState(false)
   const [form] = Form.useForm<BackendFormValues>()
 
@@ -296,13 +309,18 @@ export default function BackendsPage() {
     },
     {
       title: t('common.actions'), key: 'actions',
-      render: (_, row) => (
-        <ActionButtons
-          onEdit={() => navigate(`/backends/${row.id}`)}
-          onDelete={() => del.mutate(row.id)}
-          deleteConfirm={t('backends.deleteConfirm', { name: row.name })}
-        />
-      ),
+      render: (_, row) => {
+        const n = ruleCountForBackend(row.id)
+        return (
+          <ActionButtons
+            onEdit={() => navigate(`/backends/${row.id}`)}
+            onDelete={() => del.mutate(row.id)}
+            deleteConfirm={t('backends.deleteConfirm', { name: row.name })}
+            deleteDisabled={n > 0}
+            deleteDisabledReason={t('backends.deleteInUse', { n })}
+          />
+        )
+      },
     },
   ]