Correct me if I'm wrong but Decap CMS (previously Netlify CMS) runs in the browser and makes reads/edits via GitHub which can then trigger rebuilds and deploys, but it still needs a small server/proxy I think because CORS stops your browser communicating directly with the GitHub API. Netlify hosts a GitHub backend that proxies requests for you but now you're tied to Netlify and their pricing plan changes.
GitLab and BitBucket will have the same issue I think: https://github.com/isomorphic-git/isomorphic-git#cors-suppor...
Is there a simple solution here with minimal configuration? I guess you could use a browser extension to selectively relax CORS but that's not ideal.
It feels like a Git-based static site generator with a CMS that has Markdown editing and live previews that runs in the browser with minimal hosting/server restrictions would work for a huge number of small websites and blogs.