Replace uvicorn with gunicorn + UvicornWorker in backend, runtime,
and schedule Dockerfiles. New gunicorn.conf.py per service exposes
bind/workers/timeout/graceful_timeout as GUNICORN_* env knobs.
Notable details:
- schedule: timeout=0 (disables gunicorn worker heartbeat) so long
notebook execution isn't killed by gunicorn's silent-worker kill.
- All three configs: drop dead threads=4 setting; UvicornWorker is
async and ignores threads.
- Pin gunicorn>=26.0.0 in each pyproject; uv.lock regenerated.
- Drop stale 'COPY contracts ./contracts' from runtime and schedule
Dockerfiles (contracts dir was deleted in an earlier refactor;
builds would have failed).
- backend Dockerfile: switch to uv sync layout matching runtime/
schedule; add build deps for native wheels.
Co-Authored-By: Claude <noreply@anthropic.com>
Winnie