Add a REST API for the frontend

[see guide](https://dev.to/nditah/how-to-build-a-rest-api-with-node-prisma-and-postgresql-429a#step-5-implementing-your-first-rest-api-route)  
  
Since we wanna reuse the same schema and DB functions we should extract that stuff either into an npm (or GH) package, or into a repo linked as a submodule (TBD).