M: Application logs grow without rotation - #4

# Description

The `challenge-m.sh` script writes to the application log file but **never rotates it**.

As a result, `logs/app.log` can grow indefinitely, which may eventually consume disk space and cause operational issues.

The script must automatically handle log rotation during execution.

## Acceptance Criteria

* [ ] Check the size of `logs/app.log` during script execution
* [x] If the log file size exceeds **1MB**, rotate it
* [x] Rotated log files must be stored in the `logs/` directory
* [x] Keep **only the last 3 rotated log files**
* [ ] Automatically remove older rotated logs

## Notes

* A simple rotation strategy is sufficient
* Do **not** use external tools (e.g. `logrotate`)
* The script should continue normal execution after rotation