Add built-in GitHub tools for improved code research

Sometimes, Mux needs to research how a library/framework/external codebase works in order to impact its work. Today, I see Mux doing stuff like `curl raw.githubusercontent.com` in order to fetch these repos which is a bit slow/clunky. Blink, on the other hand, has a lovely set of built-in GitHub tools making it one of my favorite research tools.

I'm sure I could add the GitHub MCP, but figured I'd submit this feature request as it may benefit other users