phoenixframework/phoenix ? reverse-engineered prompt

I want to build a web application that can handle a massive number of users at the same time and feels really fast and interactive. The most important feature is realtime communication, so things like live notifications, chat messages, or data dashboards should update instantly without needing to refresh the page.

The backend needs to be super reliable and fault-tolerant so it can scale from a small prototype to a huge production app. I've heard that the Elixir language is great for this kind of high-concurrency work. Can you build me a complete framework for this? It should handle everything from the server-side logic and APIs to the frontend JavaScript needed to make the live features work smoothly.