StemRoller: desktop stem separator, Android stems player, and server daemons

- stemroller/: PySide6/QML desktop app and player for separating music into stems
- android/: Plex music player that plays per-stem mixes, with Android Auto support,
  a graphic + parametric (Equalizer APO-style) EQ, and offline downloads
- server/: stemserve (serves stems to the app) and stemd (separates the library on
  the server's GPU, with "Stem Now" priority requests)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/Dockerfile

@@ -0,0 +1,8 @@
+FROM python:3.12-alpine
+RUN apk add --no-cache ffmpeg
+COPY stemserve.py /app/stemserve.py
+ENV STEMS_DIR=/stems CACHE_DIR=/cache PORT=8765 PYTHONUNBUFFERED=1
+EXPOSE 8765
+# Unraid shares belong to nobody:users.
+USER 99:100
+CMD ["python", "/app/stemserve.py"]