Harden RC7 API response contracts

backend/app/api/routes/demo.py

@@ -4,6 +4,7 @@ from fastapi import APIRouter, Depends, status
 from sqlalchemy.orm import Session
 
 from app.db.session import get_db
+from app.schemas import Envelope
 from app.schemas.demo import DemoWorkflowResponse
 from app.services.demo_workflow_service import DemoWorkflowService
 from app.utils.response import envelope
@@ -11,7 +12,11 @@ from app.utils.response import envelope
 router = APIRouter(prefix="/demo", tags=["demo"])
 
 
-@router.post("/workflow", status_code=status.HTTP_201_CREATED, response_model=dict)
+@router.post(
+    "/workflow",
+    status_code=status.HTTP_201_CREATED,
+    response_model=Envelope[DemoWorkflowResponse],
+)
 def seed_demo_workflow(db: Session = Depends(get_db)) -> dict:
     result: DemoWorkflowResponse = DemoWorkflowService.seed(db)
     return envelope(result.model_dump())