feat(config): add configurable check-in date restriction and persistent logging

- Add ENABLE_CHECKIN_DATE_RESTRICTION environment variable to allow flexible check-in testing
- Replace NODE_ENV check with configurable flag in check-in validation logic
- Implement persistent logging with external Docker volumes (slc_logs_prod)
- Configure backend-prod and nginx-prod to write logs to /var/log/app/ and /var/log/nginx-app/
- Increase log rotation limits (50MB, 10 files) for better debugging
- Update .env.example files with new check-in configuration

backend/.env.production.example

@@ -71,3 +71,8 @@ CLOUDFLARE_TURN_API_TOKEN=your-production-turn-api-token-here
 # Beta Testing
 # Auto-assign SUPPORTER tier to new registrations during beta
 BETA_AUTO_SUPPORTER=false
+
+# Event Check-in
+# Enable date restriction for check-in (event dates ±1 day)
+# Set to 'false' for testing or events where QR code access is controlled manually
+ENABLE_CHECKIN_DATE_RESTRICTION=false