feat: notifications, audit logging, and admin improvements

- Add centralized notification service with webhook (Discord/Slack) and
  email (SMTP) support, triggered for trip invites, booking changes,
  collab messages, and trip reminders
- Webhook sends one message per event (group channel); email sends
  individually per trip member, excluding the actor
- Discord invite notifications now include the invited user's name
- Add LOG_LEVEL env var (info/debug) controlling console and file output
- INFO logs show user email, action, and IP for audit events; errors
  for HTTP requests
- DEBUG logs show every request with full body/query (passwords redacted),
  audit details, notification params, and webhook payloads
- Add persistent trek.log file logging with 10MB rotation (5 files)
  in /app/data/logs/
- Color-coded log levels in Docker console output
- Timestamps without timezone name (user sets TZ via Docker)
- Add Test Webhook and Save buttons to admin notification settings
- Move notification event toggles to admin panel
- Add daily trip reminder scheduler (9 AM, timezone-aware)
- Wire up booking create/update/delete and collab message notifications
- Add i18n keys for notification UI across all 13 languages

Made-with: Cursor

server/.env.example

@@ -1,6 +1,7 @@
 PORT=3000
 NODE_ENV=development
 DEBUG=false
+LOG_LEVEL=info
 
 # REQUIRED for production — generate with: openssl rand -hex 32
 JWT_SECRET=CHANGEME_GENERATE_WITH_openssl_rand_hex_32