fix(firewall): fehlende onError-Handler + i18n in Rules + NATRules

- 6 Mutations (create/update/del je Rules + NATRules) bekommen onError-Handler
- Deutsche Placeholder-Texte → t() überführt
- Action-Labels (accept/drop/reject) und Kind-Labels (any/object/group/cidr)
  in t() überführt statt hardkodiert anzeigen
- CIDR-Label-Hardkodierung in Rules-Formular behoben
- en/de: fw.rule.actions.*, fw.rule.kinds.*, fw.rule.namePlaceholder,
  fw.nat.namePlaceholder ergänzt

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

management-ui/src/pages/Firewall/NATRules.tsx

@@ -69,6 +69,7 @@ export default function NATRulesTab() {
       message.success(t('common.save')); setCreating(false); form.resetFields()
       void qc.invalidateQueries({ queryKey: ['fw', 'nat'] })
     },
+    onError: (e: Error) => message.error(e.message),
   })
   const update = useMutation({
     mutationFn: async ({ id, v }: { id: number; v: FormValues }) => { await apiClient.put(`/firewall/nat-rules/${id}`, v) },
@@ -76,10 +77,12 @@ export default function NATRulesTab() {
       message.success(t('common.save')); setEditing(null); form.resetFields()
       void qc.invalidateQueries({ queryKey: ['fw', 'nat'] })
     },
+    onError: (e: Error) => message.error(e.message),
   })
   const del = useMutation({
     mutationFn: async (id: number) => { await apiClient.delete(`/firewall/nat-rules/${id}`) },
     onSuccess: () => { void qc.invalidateQueries({ queryKey: ['fw', 'nat'] }) },
+    onError: (e: Error) => message.error(e.message),
   })
   const quickToggle = useMutation({
     mutationFn: async ({ id, row, checked }: { id: number; row: NATRule; checked: boolean }) => {
@@ -190,7 +193,7 @@ export default function NATRulesTab() {
           onFinish={(v) => { if (editing) update.mutate({ id: editing.id, v }); else create.mutate(v) }}
         >
           <Form.Item label={t('fw.nat.name')} name="name">
-            <Input placeholder="Forward HTTP zu Web-Backend" />
+            <Input placeholder={t('fw.nat.namePlaceholder')} />
           </Form.Item>
           <Space size="middle">
             <Form.Item label={t('fw.nat.priority')} name="priority" rules={[{ required: true }]}>