Yeah monetization is always tough, especially with something like this. My thoughts (were I in your position) would be to offer a full/unrestricted and open source single-player mode (open core model, with core licensed AGPLv3) that just modifies files on disk and is otherwise completely ignorant of git or anything else. Then for paid/hosted version, on top of it being hosted, you get full integration with github so PRs and diffs and things can be sent directly from the tool (which is great for designers). That also wouldn't require devs to do anything to buy in since the interface for them is just standard PR workflow.
If it were me personally, I'd probably make the whole thing ("enterprise" features and all) open sourced under AGPLed with monetization being a hosted version available for paid stuff. Make sure you own the copyright so you can relicense in the future should that become necessary. I think you still get the vast majority of users that would be willing to pay that way, but you also get that crucial group of people who want the option of ejecting from you as a vendor should you go a directin they don't like (enshittification, etc). It's also IMHO a very ethical way to do business. Register trademarks on your app's name and stuff, and defend them proactively. Worst case scenario if someone forks and tries to compete with you, at that point you exercise that copyright to relicense the different parts to the "open core" model. It isn't likely to ever be an issue, but if it did you have a move.
For targeting devs vs designers, IIWM I'd probably make the UI modal. I.e. design mode vs developer mode. Design mode can cater to designers, dev mode to devs. That way you can make UX decisions for one group that would irk the other group.