Make User a proper SQLAlchemy model so kds_course_bumps FK resolves

kds_course_bumps.bumped_by_user_id references users.id — SQLAlchemy needs
the User model in Base.metadata to resolve this at startup. Route handlers
still receive a SimpleNamespace from auth.py at runtime.

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

backend/models/user.py

@@ -21,11 +21,13 @@ class Kitchen(Base):
     )
 
 
-class User:
-    """Type stub for Depends(get_current_user) annotations — runtime is a SimpleNamespace."""
-    id: int
-    email: str
-    name: str
-    is_admin: bool
-    kitchen_id: int
-    caps: list
+class User(Base):
+    """Minimal SQLAlchemy model so FKs referencing users.id resolve at startup.
+    Route handlers receive a SimpleNamespace from auth.py at runtime, not instances
+    of this class — this definition exists only for SQLAlchemy FK resolution."""
+    __tablename__ = "users"
+
+    id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    email: Mapped[str] = mapped_column(String(255), nullable=False)
+    name: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    is_admin: Mapped[bool] = mapped_column(default=False)