My first NestJS backend: seeking good practice & code review feedback

I've just finished the core development for my first "real-world" NestJS backend and would love to get some experienced eyes on it. I've tried to follow best practices as I understand them, but I'm sure there are areas for improvement, especially around modularity, architecture, and testing.

Here is the GitHub repository:

https://github.com/Nuvix-Tech/nuvix/