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

server/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "trek-server",
-  "version": "2.6.2",
+  "version": "2.7.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "trek-server",
-      "version": "2.6.2",
+      "version": "2.7.0",
       "dependencies": {
         "archiver": "^6.0.1",
         "bcryptjs": "^2.4.3",
@@ -19,6 +19,7 @@
         "multer": "^2.1.1",
         "node-cron": "^4.2.1",
         "node-fetch": "^2.7.0",
+        "nodemailer": "^8.0.4",
         "otplib": "^12.0.1",
         "qrcode": "^1.5.4",
         "tsx": "^4.21.0",
@@ -37,6 +38,7 @@
         "@types/multer": "^2.1.0",
         "@types/node": "^25.5.0",
         "@types/node-cron": "^3.0.11",
+        "@types/nodemailer": "^7.0.11",
         "@types/qrcode": "^1.5.5",
         "@types/unzipper": "^0.10.11",
         "@types/uuid": "^10.0.0",
@@ -653,6 +655,16 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/nodemailer": {
+      "version": "7.0.11",
+      "resolved": "https://registry.npmjs.org/@types/nodemailer/-/nodemailer-7.0.11.tgz",
+      "integrity": "sha512-E+U4RzR2dKrx+u3N4DlsmLaDC6mMZOM/TPROxA0UAPiTgI0y4CEFBmZE+coGWTjakDriRsXG368lNk1u9Q0a2g==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/qrcode": {
       "version": "1.5.6",
       "resolved": "https://registry.npmjs.org/@types/qrcode/-/qrcode-1.5.6.tgz",
@@ -2520,6 +2532,15 @@
       "integrity": "sha512-O5lz91xSOeoXP6DulyHfllpq+Eg00MWitZIbtPfoSEvqIHdl5gfcY6hYzDWnj0qD5tz52PI08u9qUvSVeUBeHw==",
       "license": "MIT"
     },
+    "node_modules/nodemailer": {
+      "version": "8.0.4",
+      "resolved": "https://registry.npmjs.org/nodemailer/-/nodemailer-8.0.4.tgz",
+      "integrity": "sha512-k+jf6N8PfQJ0Fe8ZhJlgqU5qJU44Lpvp2yvidH3vp1lPnVQMgi4yEEMPXg5eJS1gFIJTVq1NHBk7Ia9ARdSBdQ==",
+      "license": "MIT-0",
+      "engines": {
+        "node": ">=6.0.0"
+      }
+    },
     "node_modules/nodemon": {
       "version": "3.1.14",
       "resolved": "https://registry.npmjs.org/nodemon/-/nodemon-3.1.14.tgz",