feat: Add daily event notification emails via cron job

- Add node-cron for scheduled tasks
- Create cron/calendar structure with:
  - email-template.js: HTML email template for event notifications
  - event-notifier.js: Logic to query tomorrow's events and send emails
  - index.js: Cron scheduler (runs daily at configurable time)
- Send notifications via JMAP using sender email from database
- Add admin endpoint POST /api/admin/trigger-notifications for testing
- Add env variables: NOTIFICATION_TIME, NOTIFICATION_SENDER_EMAIL

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -30,6 +30,7 @@
     "jsonwebtoken": "^9.0.2",
     "morgan": "^1.10.0",
     "multer": "^2.0.2",
+    "node-cron": "^4.2.1",
     "pg": "^8.16.3",
     "uuid": "^13.0.0",
     "xss-clean": "^0.1.4",