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>

pyproject.toml

@@ -3,7 +3,7 @@ requires = ["hatchling"]
 build-backend = "hatchling.build"
 
 [project]
-name = "roundtable"
+name = "steward"
 version = "0.1.0"
 requires-python = ">=3.11"
 dependencies = [
@@ -32,11 +32,11 @@ dev = [
 ]
 
 [project.scripts]
-roundtable = "roundtable.cli:main"
+steward = "steward.cli:main"
 
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
 testpaths = ["tests"]
 
 [tool.hatch.build.targets.wheel]
-packages = ["roundtable"]
+packages = ["steward"]