Moves all ~30 pipeline scripts, configs, and the vendored sldl binary into
this repo (source /opt/sldl left untouched). Removes all docker exec/docker
compose dependencies now that beets and sldl run in-process/as a subprocess
of this container instead of via soulbeet/on-demand sldl containers.
Replaces hardcoded host paths, Navidrome credentials, and Spotify credential
sourcing with env-var-driven paths and shared credential loaders. Adds
Dockerfile, entrypoint.sh, requirements.txt, docker-compose.snippet.yml, and
the initial app DB schema.
andrew