Simple. 
Discussion
Oh yeah, I agree with whoever told you you’re recreating git, which is already decentralized-first, instead of GitHub.
What needs replacing is the stuff GitHub offers on top of git
Where do you store your code repos?
Many places, but storage != revision mgmt system 😅
If it were a matter of wanting to leverage nostr relays for storage and data distribution you would probably be better off just saving git blobs on relays and leveraging git enormous, decentralized-first, architecture.
(To be clear, I don’t think that should be done)