feat(cluster): (c) Phase-3 MVP — stable node-id + self-register + Cluster-Page

Minimal-Slice für Phase-3-Cluster:
* internal/cluster/node_id.go — stable UUID 'n-<16hex>' in
  /var/lib/edgeguard/node-id, idempotent über reboots.
* internal/cluster/store.go — ha_nodes-Repo (List/Get/UpsertSelf)
  via pgxpool. EnsureSelfRegistered upsertet die lokale Row beim
  Boot mit FQDN aus setup.json.
* internal/handlers/cluster.go — GET /api/v1/cluster/nodes liefert
  alle ha_nodes plus local_id (für UI-Highlighting).
* main.go: nach DB-Pool-Open wird EnsureSelfRegistered (nur wenn
  setup.completed) ausgeführt, ClusterHandler registriert.
* management-ui/src/pages/Cluster/index.tsx — Tabelle mit Node-ID,
  FQDN, Rolle, Beitrittszeit; eigene Node mit "diese Node"-Tag
  markiert. Sidebar-Eintrag + i18n de/en.

Bewusst NICHT in dieser Runde: cluster-init/cluster-join CLIs, KeyDB
Active-Active config-gen, PG streaming replication, mTLS zwischen
Peers, License-Leader-Election. Diese kommen mit dem ersten echten
Multi-Node-Test (Phase 3.1) — sonst Code ohne Smoke-Möglichkeit.

End-to-end-Smoke: setup → restart → ha_nodes hat 1 Row mit
fqdn=eg.example.com, /cluster/nodes liefert sie korrekt mit
local_id-Markierung.

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

management-ui/src/App.tsx

@@ -16,6 +16,7 @@ const DashboardPage = lazy(() => import('./pages/Dashboard'))
 const DomainsPage = lazy(() => import('./pages/Domains'))
 const BackendsPage = lazy(() => import('./pages/Backends'))
 const RoutingRulesPage = lazy(() => import('./pages/RoutingRules'))
+const ClusterPage = lazy(() => import('./pages/Cluster'))
 const SettingsPage = lazy(() => import('./pages/Settings'))
 
 const queryClient = new QueryClient({
@@ -79,6 +80,7 @@ export default function App() {
                   <Route path="/domains" element={<DomainsPage />} />
                   <Route path="/backends" element={<BackendsPage />} />
                   <Route path="/routing-rules" element={<RoutingRulesPage />} />
+                  <Route path="/cluster" element={<ClusterPage />} />
                   <Route path="/settings" element={<SettingsPage />} />
                 </Route>
 

management-ui/src/components/Layout/Sidebar.tsx

@@ -1,4 +1,4 @@
-import { BranchesOutlined, DashboardOutlined, DatabaseOutlined, GlobalOutlined, SettingOutlined } from '@ant-design/icons'
+import { ApartmentOutlined, BranchesOutlined, DashboardOutlined, DatabaseOutlined, GlobalOutlined, SettingOutlined } from '@ant-design/icons'
 import { Menu, Typography } from 'antd'
 import { useNavigate, useLocation } from 'react-router-dom'
 import { useTranslation } from 'react-i18next'
@@ -13,6 +13,7 @@ export default function Sidebar() {
     { key: '/domains', icon: <GlobalOutlined />, label: t('nav.domains') },
     { key: '/backends', icon: <DatabaseOutlined />, label: t('nav.backends') },
     { key: '/routing-rules', icon: <BranchesOutlined />, label: t('nav.routing') },
+    { key: '/cluster', icon: <ApartmentOutlined />, label: t('nav.cluster') },
     { key: '/settings', icon: <SettingOutlined />, label: t('nav.settings') },
   ]
 

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

@@ -83,6 +83,15 @@
     "selectBackend": "Backend wählen",
     "deleteConfirm": "Diese Routing-Regel wirklich löschen?"
   },
+  "cluster": {
+    "title": "Cluster",
+    "intro": "{{count}} Node(s) registriert. Multi-Node-Cluster (KeyDB Active-Active + PG Streaming Replication) folgt in einem späteren Release.",
+    "id": "Node-ID",
+    "fqdn": "FQDN",
+    "role": "Rolle",
+    "joinedAt": "Beigetreten",
+    "self": "diese Node"
+  },
   "settings": {
     "title": "Einstellungen",
     "intro": "System-Information und Setup-Status. Bearbeitbare Werte folgen in einem späteren Release.",

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

@@ -83,6 +83,15 @@
     "selectBackend": "Select backend",
     "deleteConfirm": "Really delete this routing rule?"
   },
+  "cluster": {
+    "title": "Cluster",
+    "intro": "{{count}} node(s) registered. Multi-node cluster (KeyDB Active-Active + PG streaming replication) coming in a later release.",
+    "id": "Node ID",
+    "fqdn": "FQDN",
+    "role": "Role",
+    "joinedAt": "Joined",
+    "self": "this node"
+  },
   "settings": {
     "title": "Settings",
     "intro": "System information and setup status. Editable values come in a later release.",

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

@@ -0,0 +1,74 @@
+import { Card, Spin, Table, Tag, Typography } from 'antd'
+import type { ColumnsType } from 'antd/es/table'
+import { useQuery } from '@tanstack/react-query'
+import { useTranslation } from 'react-i18next'
+
+import apiClient, { isEnvelope } from '../../api/client'
+
+interface HANode {
+  id: string
+  name: string
+  fqdn: string
+  api_url: string
+  public_ip?: string | null
+  internal_ip?: string | null
+  role: string
+  last_seen?: string | null
+  joined_at: string
+  created_at: string
+  updated_at: string
+}
+
+interface ClusterPayload {
+  nodes: HANode[]
+  local_id: string
+}
+
+export default function ClusterPage() {
+  const { t } = useTranslation()
+
+  const { data, isLoading } = useQuery({
+    queryKey: ['cluster', 'nodes'],
+    queryFn: async () => {
+      const r = await apiClient.get('/cluster/nodes')
+      if (isEnvelope(r.data)) return r.data.data as ClusterPayload
+      return null
+    },
+    refetchInterval: 30_000,
+  })
+
+  if (isLoading) return <Spin />
+
+  const columns: ColumnsType<HANode> = [
+    {
+      title: t('cluster.id'), dataIndex: 'id', key: 'id',
+      render: (id: string) => (
+        <span>
+          <code>{id}</code>{' '}
+          {id === data?.local_id && <Tag color="blue">{t('cluster.self')}</Tag>}
+        </span>
+      ),
+    },
+    { title: t('cluster.fqdn'), dataIndex: 'fqdn', key: 'fqdn' },
+    { title: t('cluster.role'), dataIndex: 'role', key: 'role' },
+    { title: t('cluster.joinedAt'), dataIndex: 'joined_at', key: 'joined_at',
+      render: (s: string) => new Date(s).toLocaleString() },
+  ]
+
+  return (
+    <div>
+      <Typography.Title level={3}>{t('cluster.title')}</Typography.Title>
+      <Typography.Paragraph type="secondary">
+        {t('cluster.intro', { count: data?.nodes.length ?? 0 })}
+      </Typography.Paragraph>
+      <Card>
+        <Table
+          rowKey="id"
+          columns={columns}
+          dataSource={data?.nodes ?? []}
+          pagination={false}
+        />
+      </Card>
+    </div>
+  )
+}