Add Kitchen SQLAlchemy model to models/user.py

settings.py imports Kitchen for the back-reference relationship on
KitchenSettings.kitchen. KDS uses kitchen_db directly so the table exists;
this minimal model satisfies the import without pulling in kitchen-only models.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/models/user.py

@@ -1,11 +1,28 @@
 """
-Type stub — kds.py has `from models.user import User` for the type annotation on
-Depends(get_current_user). At runtime the dependency returns a SimpleNamespace from
-auth.py; this class satisfies the import without pulling in the full SQLAlchemy model.
+Minimal SQLAlchemy models for KDS. KDS uses kitchen_db directly so these
+tables already exist — these definitions just allow relationship navigation.
 """
+from datetime import datetime
+from sqlalchemy import String, DateTime
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from database import Base
+
+
+class Kitchen(Base):
+    __tablename__ = "kitchens"
+
+    id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow)
+
+    settings: Mapped["KitchenSettings"] = relationship(
+        "KitchenSettings", back_populates="kitchen", uselist=False
+    )
 
 
 class User:
+    """Type stub for Depends(get_current_user) annotations — runtime is a SimpleNamespace."""
     id: int
     email: str
     name: str