feat(ai): add tenant-safe hierarchical expense learning

server/src/app/api/deps.py

@@ -26,6 +26,7 @@ class CurrentUserContext:
     is_admin: bool
     tenant_id: str = "default"
     department_name: str = ""
+    department_id: str = ""
     cost_center: str = ""
     position: str = ""
     grade: str = ""
@@ -74,6 +75,7 @@ def _authenticate_bearer_user(db: Session, authorization: str | None) -> Current
         is_admin=user.is_admin,
         tenant_id=user.tenant_id,
         department_name=user.department,
+        department_id=user.department_id or "",
         cost_center=user.cost_center,
         position=user.position,
         grade=user.grade,