refactor(domains): Einstellung Standard-Nameserver entfernt, Doku angepasst (h3t)

- Spalte DomainsConfig.defaultNameServers per Migration 20261008160000 entfernt
- Feld in Einstellungen/Status (API, DTO, Typen) und Karte im Web entfernt
- Anleitungen und CHANGELOG: Nameserver kommen aus AutoDNS

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/web/src/app/(portal)/modules/domains/domains-page.test.tsx

@@ -70,7 +70,6 @@ function status(over: Partial<DomainsStatus> = {}): DomainsStatus {
     configured: true,
     demoConfigured: true,
     liveConfigured: false,
-    defaultNameServers: [],
     ...over,
   };
 }
@@ -80,7 +79,6 @@ function settings(over: Partial<DomainsSettings> = {}): DomainsSettings {
     environment: 'DEMO',
     demo: { user: 'api-user', hasPassword: true, context: 1 },
     live: { user: null, hasPassword: false, context: null },
-    defaultNameServers: [],
     configured: { demo: true, live: false },
     ...over,
   };
@@ -354,19 +352,11 @@ describe('Einstellungen', () => {
     expect(within(demoCard).getByText('Bitte zuerst speichern')).toBeTruthy();
   });
 
-  it('Nameserver: speichert die bereinigte Liste', async () => {
+  it('Einstellungen zeigen keine Karte "Standard-Nameserver" mehr (h3t)', async () => {
     await renderSettings();
-    const first = (await screen.findByLabelText('Nameserver 1')) as HTMLInputElement;
-    fireEvent.change(first, { target: { value: ' NS1.Example.com ' } });
-    fireEvent.change(screen.getByLabelText('Nameserver 2'), {
-      target: { value: 'ns2.example.com' },
-    });
-    const card = document.getElementById('domains-nameservers') as HTMLElement;
-    fireEvent.click(within(card).getByRole('button', { name: 'Speichern' }));
-    await waitFor(() => expect(mockSaveSettings).toHaveBeenCalledTimes(1));
-    expect(mockSaveSettings).toHaveBeenCalledWith({
-      defaultNameServers: ['ns1.example.com', 'ns2.example.com'],
-    });
+    await screen.findByRole('radio', { name: /Live-System \(kostenpflichtig\)/ });
+    expect(screen.queryByText('Standard-Nameserver')).toBeNull();
+    expect(document.getElementById('domains-nameservers')).toBeNull();
   });
 });