feat(license): Lizenz-System mit Ed25519-Verify gegen license.netcell-it.com

Portiert mail-gateway/internal/license (Verify, Cache, Trial, Signature)
+ DB-Mirror (internal/services/license) + REST-Handler (status/verify/key/clear)
+ UI-Page /license (Activate, Status, Limits, Features, Re-verify)
+ <LicenseBanner /> neben UpdateBanner (trial-expiring, expired, verify-failed)
+ Scheduler: täglich Re-verify (24h-Tick)

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

management-ui/src/App.tsx

@@ -25,6 +25,7 @@ const ForwardProxyPage = lazy(() => import('./pages/ForwardProxy'))
 const DNSPage = lazy(() => import('./pages/DNS'))
 const NTPPage = lazy(() => import('./pages/NTP'))
 const ClusterPage = lazy(() => import('./pages/Cluster'))
+const LicensePage = lazy(() => import('./pages/License'))
 const SettingsPage = lazy(() => import('./pages/Settings'))
 
 const queryClient = new QueryClient({
@@ -108,6 +109,7 @@ export default function App() {
                 <Route path="/dns" element={<DNSPage />} />
                 <Route path="/ntp" element={<NTPPage />} />
                   <Route path="/cluster" element={<ClusterPage />} />
+                  <Route path="/license" element={<LicensePage />} />
                   <Route path="/settings" element={<SettingsPage />} />
                 </Route>