Havenox/mixer8 ? reverse-engineered prompt

Build me a music streaming app where each song plays as separate stems in perfect sync, so I can control vocals, bass, drums, keys, and other parts like a simple mixing desk.

I want a clean web app with a persistent player, a track page, and easy controls for volume and mix presets in real time. It should feel like a modern streaming service, but with a DAW style mixer for each song. Also build the backend and API to manage tracks, stems, login, access control, and saved mix settings, plus a PostgreSQL database for the data.

If possible, include the automation service that can upload audio to an external stem separation site, wait for processing, and download the isolated stems automatically. Use Docker so I can run the whole thing locally, and look up current docs online if you need to.