fix(routers+imports): fix missing DetectionRule import and correct -> list return type annotations that actually return paginated dicts

backend/app/routers/snapshots.py

@@ -87,7 +87,7 @@ def list_snapshots(
     db: Session = Depends(get_db),
     # Entry: current_user
     current_user: User = Depends(get_current_user),
-) -> list:
+) -> dict:
     """List coverage snapshots ordered by creation date (newest first)."""
     # Return list_snapshots_svc(db, offset=offset, limit=limit)
     return list_snapshots_svc(db, offset=offset, limit=limit)