chore: rename project Roundtable → Steward

Renames the Python package directory, CLI command, env var prefix,
docker-compose service/container/image, Postgres role/db, and all
visible branding. Marketing form is "Fabled Steward".

Clean break from the previous rebrand: drops the fabledscryer→roundtable
import shim in __init__.py and the FABLEDSCRYER_* env var fallback in
config.py and migrations/env.py. Env vars are now STEWARD_* only.

Heads-up for existing deployments:
- Postgres user/db renamed fabledscryer → steward in docker-compose.yml.
  Existing volumes need the role/db renamed inside Postgres, or override
  POSTGRES_USER/POSTGRES_DB to keep the old names.
- Host-agent systemd unit is now steward-agent.service. Existing agents
  keep running under the old name; reinstall to switch.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Dockerfile

@@ -13,7 +13,7 @@ RUN pip install --upgrade pip
 WORKDIR /app
 
 COPY pyproject.toml .
-COPY roundtable/ roundtable/
+COPY steward/ steward/
 RUN pip install --no-cache-dir .
 
 COPY alembic.ini .
@@ -22,7 +22,7 @@ RUN chmod +x /entrypoint.sh
 
 # Runtime directories — owned by app user. The container starts as root
 # so the entrypoint can fix up /data permissions if needed, then drops to
-# 'app' (uid 1000) via gosu before launching roundtable.
+# 'app' (uid 1000) via gosu before launching steward.
 RUN useradd -m -u 1000 app \
     && mkdir -p /data/playbook_cache /data/plugins \
     && chown -R app:app /data /app
@@ -30,4 +30,4 @@ RUN useradd -m -u 1000 app \
 EXPOSE 5000
 
 ENTRYPOINT ["/entrypoint.sh"]
-CMD ["roundtable", "--host", "0.0.0.0", "--port", "5000"]
+CMD ["steward", "--host", "0.0.0.0", "--port", "5000"]