It's not just a web front end. I would call it a software development lifecycle service. On top of repos for source code management there could be a bunch of services: Issue tracker, CI/CD automation, static pages hosting, flexible permissions system, even pull requests - all this is not Git.

Forge is a nice and easy name, but not sure if many people realize what it means or recognize that meaning.

"Git hosting" would be more appropriate. Unless that by frontend, you mean specifically web frontend, but that would be weird, because forges also provide the web backend part.

Sourceforge was the biggest FOSS host in the 2000s, before GitHub (mainly because there was not much centralization to begin with). That train is long gone. :) Sure, the name and website Sourceforge still exist. Myspace, Digg and Yahoo do too. They are basically web ghosts, only an echo of what they once were.

Its not a fronted, you don't purely commit and manage code from github. It's a platform for hosting git repositories that supports integration with CI/CD tools. At its heart git is simple (enough), it's a version control software. Github is a Web platform that hosts projects version controlled with git and adds in features like pull requests and reviews or github actions for building/linting your project.