Fix PackageArtifactResponse missing sha256 and version fields

- Add sha256 field to list_package_artifacts response (artifact ID is SHA256)
- Add version field to PackageArtifactResponse schema
- Add version field to frontend PackageArtifact type
- Update getArtifactVersion to prefer direct version field

backend/app/schemas.py

@@ -256,6 +256,7 @@ class PackageArtifactResponse(BaseModel):
     created_at: datetime
     created_by: str
     format_metadata: Optional[Dict[str, Any]] = None
+    version: Optional[str] = None  # Version from PackageVersion if exists
 
     class Config:
         from_attributes = True