fix(clean-release): replace absolute backend imports for runtime packaging

backend/src/services/clean_release/dto.py

@@ -6,7 +6,7 @@
 from datetime import datetime
 from typing import List, Optional, Dict, Any
 from pydantic import BaseModel, Field
-from backend.src.services.clean_release.enums import CandidateStatus, RunStatus, ComplianceDecision
+from src.services.clean_release.enums import CandidateStatus, RunStatus, ComplianceDecision
 
 class CandidateDTO(BaseModel):
     """DTO for ReleaseCandidate."""