signalapp/Signal-Server ? reverse-engineered prompt

Build me the backend server for the Signal Private Messenger app. My goal is to run a self-hosted, private messaging service that's compatible with the official Signal clients on Android, iOS, and desktop. The server needs to handle all the core functionality for secure, end-to-end encrypted communication.

I know the official server is written in Java and uses Maven. The big dependency I saw mentioned is something called FoundationDB, so you'll need to make sure that's properly installed and configured for the server to work. Please set up the complete project, install all the required dependencies, and make sure it can be built and tested successfully. You can look up the official protocol documentation on the Signal website if you need more details on how it all works.