Redis appendfsync blocking causes Gunicorn worker timeout

When Redis cache grows to several hundred MB and appendfsync is set to 'everysec', disk write operations can take over 1 second, blocking Gunicorn worker processes and triggering WORKER TIMEOUT errors, resulting in 502 errors to clients.

Change Redis configuration from 'appendfsync everysec' to 'appendfsync no' to prevent blocking synchronous writes to disk. This allows Redis to write asynchronously without blocking Gunicorn workers.