Here's this too from Oleg as he commented on something adjacent to your question somewhere else:
It is achieved by using data as a source of truth, not the code. Web tooling is very fragmented. People have too many opinions on how to write components and that makes it nearly impossible to have components written by hand and then synced back into the UI without enforcing a huge amount of constraints. You will end up writing code in such a way that the UI can handle.
To your second question, Webstudio provides the frontend but you can use any backend like headlesses CMSs for example. The Webstudio architecture currently outputs a Remix app (or static if you so choose), though it is written to support other frameworks as well.. we just haven't gotten there
