feat: email notifications, webhook support, ICS export — closes #110

Email Notifications:
- SMTP configuration in Admin > Settings (host, port, user, pass, from)
- App URL setting for email CTA links
- Webhook URL support (Discord, Slack, custom)
- Test email button with SMTP validation
- Beautiful HTML email template with TREK logo, slogan, red heart footer
- All notification texts translated in 8 languages (en/de/fr/es/nl/ru/zh/ar)
- Emails sent in each user's language preference

Notification Events:
- Trip invitation (member added)
- Booking created (new reservation)
- Vacay fusion invite
- Photos shared (Immich)
- Collab chat message
- Packing list category assignment

User Notification Preferences:
- Per-user toggle for each event type in Settings
- Addon-aware: Vacay/Collab/Photos toggles hidden when addon disabled
- Webhook opt-in per user

ICS Calendar Export:
- Download button next to PDF in day plan header
- Exports trip dates + all reservations with details
- Compatible with Google Calendar, Apple Calendar, Outlook

Technical:
- Nodemailer for SMTP
- notification_preferences DB table with per-event columns
- GET/PUT /auth/app-settings for admin config persistence
- POST /notifications/test-smtp for validation
- Dynamic imports for non-blocking notification sends

client/src/i18n/translations/de.ts

@@ -140,6 +140,21 @@ const de: Record<string, string | { name: string; category: string }[]> = {
   'settings.timeFormat': 'Zeitformat',
   'settings.routeCalculation': 'Routenberechnung',
   'settings.blurBookingCodes': 'Buchungscodes verbergen',
+  'settings.notifications': 'Benachrichtigungen',
+  'settings.notifyTripInvite': 'Trip-Einladungen',
+  'settings.notifyBookingChange': 'Buchungsänderungen',
+  'settings.notifyTripReminder': 'Trip-Erinnerungen',
+  'settings.notifyVacayInvite': 'Vacay Fusion-Einladungen',
+  'settings.notifyPhotosShared': 'Geteilte Fotos (Immich)',
+  'settings.notifyCollabMessage': 'Chat-Nachrichten (Collab)',
+  'settings.notifyPackingTagged': 'Packliste: Zuweisungen',
+  'settings.notifyWebhook': 'Webhook-Benachrichtigungen',
+  'admin.smtp.title': 'E-Mail & Benachrichtigungen',
+  'admin.smtp.hint': 'SMTP-Konfiguration für E-Mail-Benachrichtigungen. Optional: Webhook-URL für Discord, Slack, etc.',
+  'admin.smtp.testButton': 'Test-E-Mail senden',
+  'admin.smtp.testSuccess': 'Test-E-Mail erfolgreich gesendet',
+  'admin.smtp.testFailed': 'Test-E-Mail fehlgeschlagen',
+  'dayplan.icsTooltip': 'Kalender exportieren (ICS)',
   'settings.on': 'An',
   'settings.off': 'Aus',
   'settings.account': 'Konto',

client/src/i18n/translations/en.ts

@@ -140,6 +140,21 @@ const en: Record<string, string | { name: string; category: string }[]> = {
   'settings.timeFormat': 'Time Format',
   'settings.routeCalculation': 'Route Calculation',
   'settings.blurBookingCodes': 'Blur Booking Codes',
+  'settings.notifications': 'Notifications',
+  'settings.notifyTripInvite': 'Trip invitations',
+  'settings.notifyBookingChange': 'Booking changes',
+  'settings.notifyTripReminder': 'Trip reminders',
+  'settings.notifyVacayInvite': 'Vacay fusion invitations',
+  'settings.notifyPhotosShared': 'Shared photos (Immich)',
+  'settings.notifyCollabMessage': 'Chat messages (Collab)',
+  'settings.notifyPackingTagged': 'Packing list: assignments',
+  'settings.notifyWebhook': 'Webhook notifications',
+  'admin.smtp.title': 'Email & Notifications',
+  'admin.smtp.hint': 'SMTP configuration for email notifications. Optional: Webhook URL for Discord, Slack, etc.',
+  'admin.smtp.testButton': 'Send test email',
+  'admin.smtp.testSuccess': 'Test email sent successfully',
+  'admin.smtp.testFailed': 'Test email failed',
+  'dayplan.icsTooltip': 'Export calendar (ICS)',
   'settings.on': 'On',
   'settings.off': 'Off',
   'settings.account': 'Account',