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-lock.json

@@ -22,6 +22,7 @@
         "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",
@@ -6431,6 +6432,15 @@
         "node": ">= 0.6"
       }
     },
+    "node_modules/node-cron": {
+      "version": "4.2.1",
+      "resolved": "https://registry.npmjs.org/node-cron/-/node-cron-4.2.1.tgz",
+      "integrity": "sha512-lgimEHPE/QDgFlywTd8yTR61ptugX3Qer29efeyWw2rv259HtGBNn1vZVmp8lB9uo9wC0t/AT4iGqXxia+CJFg==",
+      "license": "ISC",
+      "engines": {
+        "node": ">=6.0.0"
+      }
+    },
     "node_modules/node-int64": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/node-int64/-/node-int64-0.4.0.tgz",