feat(backends): WebSocket-Toggle pro Backend

Migration 0017 fügt backends.websocket BOOL. Wenn aktiv emittiert der
HAProxy-Renderer `timeout tunnel 1h` IM Backend-Block; defaults-Section
hat den Global-Timeout dafür verloren. Backends ohne WS-Workload bleiben
bei strikten HTTP-Timeouts (Connection-Hygiene). Migrations-Heuristik
schaltet vm-pool/proxmox/console/vnc-Namen auto auf true damit Proxmox-
Konsole nach Deploy weiterhin durchläuft.

UI: Switch im Backend-Modal + WS-Tag in der Übersichtstabelle.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -22,6 +22,7 @@ interface Backend {
   scheme: string
   health_check_path?: string | null
   lb_algorithm: 'roundrobin' | 'leastconn' | 'source'
+  websocket: boolean
   active: boolean
   created_at: string
   updated_at: string
@@ -43,6 +44,7 @@ interface BackendFormValues {
   scheme: 'http' | 'https'
   health_check_path?: string
   lb_algorithm: 'roundrobin' | 'leastconn' | 'source'
+  websocket: boolean
   active: boolean
   domain_ids?: number[]
 }
@@ -193,7 +195,12 @@ export default function BackendsPage() {
     },
     {
       title: t('backends.lbAlgo'), dataIndex: 'lb_algorithm', key: 'lb',
-      render: (v: string) => <Tag>{v}</Tag>,
+      render: (v: string, row) => (
+        <Space size={4}>
+          <Tag>{v}</Tag>
+          {row.websocket && <Tag color="cyan">WS</Tag>}
+        </Space>
+      ),
     },
     { title: t('backends.healthCheck'), dataIndex: 'health_check_path', key: 'hc', render: (v?: string) => v ?? '—' },
     {
@@ -216,6 +223,7 @@ export default function BackendsPage() {
               scheme: row.scheme as 'http' | 'https',
               health_check_path: row.health_check_path ?? undefined,
               lb_algorithm: row.lb_algorithm,
+              websocket: row.websocket,
               active: row.active,
               domain_ids: domainsForBackend(row.id).map(d => d.id),
             })
@@ -246,7 +254,7 @@ export default function BackendsPage() {
         extraActions={
           <Button type="primary" icon={<PlusOutlined />} onClick={() => {
             setCreating(true); form.resetFields()
-            form.setFieldsValue({ scheme: 'http', lb_algorithm: 'roundrobin', active: true })
+            form.setFieldsValue({ scheme: 'http', lb_algorithm: 'roundrobin', websocket: false, active: true })
           }}>
             {t('backends.addBackend')}
           </Button>
@@ -294,6 +302,10 @@ export default function BackendsPage() {
           <Form.Item label={t('backends.healthCheck')} name="health_check_path">
             <Input placeholder="/health" />
           </Form.Item>
+          <Form.Item label={t('backends.websocket')} name="websocket" valuePropName="checked"
+            extra={t('backends.websocketHint')}>
+            <Switch />
+          </Form.Item>
           <Form.Item label={t('backends.active')} name="active" valuePropName="checked">
             <Switch />
           </Form.Item>