Add University of Cagliari to the list of institutions

There are several CS PhD programs at the University of Cagliari (Italy)

* University Website: https://en.unica.it/en
* Engineering faculty: https://unica.coursecatalogue.cineca.it/corsi/2025/11044
* Mathematics and Computer Science faculty: https://unica.coursecatalogue.cineca.it/corsi/2025/11046

Please, add it and I will then create a PR with the faculty members. Thanks!
