Production image had no DB migration step, so a fresh container had an
empty database: the durable worker queried the 'jobs' table before it
existed and crash-looped with sqlalchemy OperationalError 'no such table:
jobs' (supervisor restart loop).
- Add backend/docker_entrypoint.sh: fail-fast if DATABASE_URL is unset,
run 'alembic upgrade head' (idempotent), then exec supervisord.
- Dockerfile CMD now runs the entrypoint.
- supervisor: fix nodaemon typo, stream stdout/stderr to /dev/stdout +
/dev/stderr so worker errors are visible in container logs, and give
worker startsecs/startretries.
Verified locally: entrypoint bash syntax ok, alembic upgrade head
idempotent, jobs + 19 tables created, worker --once exits 0 after migrate
(previously exit 1 with no-such-table). Worker/schema tests 11 passed.
