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>

steward/models/users.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+import enum
+import uuid
+from datetime import datetime, timezone
+from sqlalchemy import Boolean, DateTime, Enum, String
+from sqlalchemy.orm import Mapped, mapped_column
+from .base import Base
+
+
+class UserRole(str, enum.Enum):
+    admin = "admin"
+    operator = "operator"
+    viewer = "viewer"
+
+
+class User(Base):
+    __tablename__ = "users"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    username: Mapped[str] = mapped_column(String(64), unique=True, nullable=False)
+    email: Mapped[str] = mapped_column(String(255), unique=True, nullable=False)
+    password_hash: Mapped[str] = mapped_column(String(255), nullable=False)
+    role: Mapped[UserRole] = mapped_column(Enum(UserRole), nullable=False, default=UserRole.viewer)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), nullable=False, default=lambda: datetime.now(timezone.utc)
+    )
+    is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)