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>

tests/test_config.py

@@ -1,25 +1,25 @@
 import os
 import textwrap
 import pytest
-from roundtable.config import load_bootstrap
+from steward.config import load_bootstrap
 
 
 def test_load_bootstrap_from_yaml(tmp_path):
     cfg_file = tmp_path / "config.yaml"
     cfg_file.write_text(textwrap.dedent("""\
         database:
-          url: postgresql+asyncpg://user:pass@localhost/roundtable
+          url: postgresql+asyncpg://user:pass@localhost/steward
         secret_key: test-secret
     """))
     cfg = load_bootstrap(cfg_file)
-    assert cfg["database_url"] == "postgresql+asyncpg://user:pass@localhost/roundtable"
+    assert cfg["database_url"] == "postgresql+asyncpg://user:pass@localhost/steward"
     assert cfg["secret_key"] == "test-secret"
 
 
 def test_env_var_database_url_overrides_yaml(tmp_path, monkeypatch):
     cfg_file = tmp_path / "config.yaml"
     cfg_file.write_text("database:\n  url: original\nsecret_key: s\n")
-    monkeypatch.setenv("FABLEDSCRYER_DATABASE_URL", "overridden")
+    monkeypatch.setenv("STEWARD_DATABASE_URL", "overridden")
     cfg = load_bootstrap(cfg_file)
     assert cfg["database_url"] == "overridden"
 
@@ -27,7 +27,7 @@ def test_env_var_database_url_overrides_yaml(tmp_path, monkeypatch):
 def test_env_var_secret_key_overrides_yaml(tmp_path, monkeypatch):
     cfg_file = tmp_path / "config.yaml"
     cfg_file.write_text("database:\n  url: x\nsecret_key: from-yaml\n")
-    monkeypatch.setenv("FABLEDSCRYER_SECRET_KEY", "from-env")
+    monkeypatch.setenv("STEWARD_SECRET_KEY", "from-env")
     cfg = load_bootstrap(cfg_file)
     assert cfg["secret_key"] == "from-env"