- Add sha256 field to API responses as explicit alias of artifact id
- Add checksum_sha1 and s3_etag fields to artifacts table
- Compute MD5, SHA1, and capture S3 ETag during upload
- Update StorageResult to return all checksums from storage layer
- Add migration 003_checksum_fields.sql for existing databases
- Add Dockerfile.local and docker-compose.local.yml for local development
- Update schemas to include all checksum fields in responses
