Code review for Barbershop bot project

Hello everyone!
In a nutshell, I was looking for a topic for a capstone project for the Ukrainian Rust Programming Bootcamp.

And then it so happened that my friend is opening a barbershop in the near future, and here threw me an idea to create a bot to record the service.

Now he uses a paid version, but I wanted to create my own version in the future with more functionality and so on.

I'll be grateful for your code reviews.

The project is not finished yet, for now I would like to start with this for starters: