If you don’t need CI/CD I’m not sure why you need a centralized frontend at all. Git itself is distributed and you can setup any code flow you can think of. It has hooks that can be used to set up code quality checks on select branches. There are local history browser apps for every platform and IDE plugins.
A frontend is no substitute for developer communication — usually what the “PR” thing does is sugarcoat the fact the devs don’t know how to use Git and/or don’t talk to each other.