feat(settings): hide the notes rights while MCP is off, mention notes in the API intro

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/settings/__tests__/ApiKeysPanel.test.tsx

@@ -67,6 +67,7 @@ describe('ApiKeysPanel', () => {
     render(<ApiKeysPanel />);
     await act(async () => {});
     expect(screen.queryByRole('tab', { name: /KI-Agenten/ })).toBeNull();
+    expect(screen.queryByRole('switch', { name: 'Notizen lesen' })).toBeNull();
     expect(screen.getAllByText(/tasks\?due=today&status=open/).length).toBeGreaterThan(0);
   });