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/src/routes/events.js

@@ -239,9 +239,9 @@ router.post('/checkin/:token', authenticate, async (req, res, next) => {
 
     const event = checkinToken.event;
 
-    // Validate dates (only in production)
-    const isProduction = process.env.NODE_ENV === 'production';
-    if (isProduction) {
+    // Validate dates (only if date restriction is enabled)
+    const enableDateRestriction = process.env.ENABLE_CHECKIN_DATE_RESTRICTION === 'true';
+    if (enableDateRestriction) {
       const now = new Date();
       const validFrom = new Date(event.startDate);
       validFrom.setDate(validFrom.getDate() - 1);