carousel : move away from keen slider

# Summary

Keen slider seems no longer maintained : https://github.com/rcbyr/keen-slider/


## Contenders

### Embla carousel

https://www.embla-carousel.com/

- reco by shadcn
- doc seems good and furnished
- lightweight

### Swiper

https://swiperjs.com/react

- well-known
- doc seems ok