Fix Artifact model field names in PyPI proxy

Use correct Artifact model fields:
- original_name instead of filename
- Add required created_by and s3_key fields
- Include checksum fields from storage result

backend/app/pypi_proxy.py

@@ -469,10 +469,15 @@ async def pypi_download_file(
             # Create artifact record
             new_artifact = Artifact(
                 id=sha256,
-                filename=filename,
+                original_name=filename,
                 content_type=content_type,
                 size=size,
                 ref_count=1,
+                created_by="pypi-proxy",
+                s3_key=result.s3_key,
+                checksum_md5=result.md5,
+                checksum_sha1=result.sha1,
+                s3_etag=result.s3_etag,
             )
             db.add(new_artifact)
             db.flush()