fix: Resolve TypeScript errors and apply database migration for email-optional

- Add Prisma import for JsonNull filter
- Fix async/await for calculateDistance function
- Install mysql2 for database operations
- Apply ALTER TABLE migration to make email nullable in database
- Verify all tests pass successfully

Tests confirm:
- Users can be created without email
- Notifications work for users without email
- Email sending gracefully skipped when no email present
- Database queries correctly filter by email presence

server/package.json

@@ -31,6 +31,7 @@
     "helmet": "^8.0.0",
     "json2csv": "^6.0.0-alpha.2",
     "multer": "^1.4.5-lts.1",
+    "mysql2": "^3.15.3",
     "node-cron": "^4.2.1",
     "nodemailer": "^7.0.10",
     "redis": "^5.9.0",