Turn the bot from a bare nohup process (silently dies on a Spark reboot) into a docker-compose service. Dockerfile bundles backend/matrix_intake + the stdlib backend/ingest Spark client it reuses; .env is mounted read-only at runtime, never baked. The existing repo-root .dockerignore (shared with the s9pk build) already keeps data/ and .env out of context. Also adds a handoff doc for wiring a spark-control dashboard card in a later session.