Phase 4: Webhooks, Backup/Restore UI, Onboarding/Tutorial

- Webhooks Backend: model, schema, service (HMAC-SHA256, httpx), routes, event bus dispatcher, migration 0042
- Webhooks Frontend: SettingsWebhooksPage (CRUD, test button, event multi-select), API client
- Backup/Restore Backend: model, schema, service (pg_dump/pg_restore), routes (admin-only), migration 0043
- Backup/Restore Frontend: SettingsBackupPage (create, list, restore dialog with RESTORE confirmation, auto-refresh)
- Onboarding: OnboardingTour (8 steps, custom CSS overlay), WelcomeDialog, onboardingStore (zustand + localStorage)
- Onboarding integrated into AppShell
- Routes: /settings/webhooks, /settings/backup registered
- Settings nav: Webhooks, Backup & Restore entries added
- Migration conflict fixed: 0042_webhooks → 0043_backups chain

frontend/src/pages/Settings.tsx

@@ -22,6 +22,8 @@ export function SettingsPage() {
     { to: '/settings/ai-settings', label: 'KI Einstellungen', icon: '\ud83e\udde0' },
     { to: '/settings/notifications', label: t('settings.notifications'), icon: '\ud83d\udd14' },
     { to: '/settings/custom-fields', label: 'Custom Fields', icon: '\ud83d\udccb' },
+    { to: '/settings/webhooks', label: 'Webhooks', icon: '\ud83d\udd14' },
+    { to: '/settings/backup', label: 'Backup & Restore', icon: '\ud83d\udcbe' },
   ];
 
   const existingPaths = new Set(hardcodedNavItems.map(item => item.to));