feat: Registrierungs-Disclaimer und Header-Zugang

Neue Accounts sehen vor dem Onboarding Hinweise zu E2E, PWA, Sync und Haftung;
bestehende Nutzer können den Disclaimer jederzeit über einen Header-Button öffnen.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/components/LogbookDashboard.tsx

@@ -7,6 +7,7 @@ import { logoutUser } from '../services/auth.js'
 import { useDialog } from './ModalDialog.tsx'
 import AccountDangerZone from './AccountDangerZone.tsx'
 import { BookOpen, Plus, Trash2, LogOut, Languages, RefreshCw, Ship, User, Wifi, WifiOff } from 'lucide-react'
+import DisclaimerHeaderButton from './DisclaimerHeaderButton.tsx'
 
 interface LogbookDashboardProps {
   onSelectLogbook: (id: string, title: string) => void
@@ -149,6 +150,8 @@ export default function LogbookDashboard({ onSelectLogbook, onLogout }: LogbookD
             <Languages size={18} />
           </button>
 
+          <DisclaimerHeaderButton />
+
           {/* Logout */}
           <button className="btn-icon logout" onClick={handleLogout} title={t('dashboard.logout')}>
             <LogOut size={18} />