Rewrite with langgraph

[Und3rf10w]

I've been using langgraph extensively, and believe that OpenJanus is a great application for it. Rewrite OpenJanus to use Langgraph architecture, which would also bring us up to speed with LCEL. For the elevenlabs callback handler, can use something like this: https://gist.github.com/Und3rf10w/b15539071fc477acf40a3e1a4f058a7f