Store SHA256 checksums with artifacts and add multiple hash support

- 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

migrations/003_checksum_fields.sql

@@ -0,0 +1,12 @@
+-- Migration 003: Additional Checksum Fields
+-- Adds checksum_sha1 and s3_etag fields to artifacts table
+
+-- ============================================
+-- Artifacts: Add checksum_sha1 and s3_etag fields
+-- ============================================
+ALTER TABLE artifacts ADD COLUMN IF NOT EXISTS checksum_sha1 VARCHAR(40);
+ALTER TABLE artifacts ADD COLUMN IF NOT EXISTS s3_etag VARCHAR(64);
+
+-- Create indexes for checksum lookups (optional, for verification queries)
+CREATE INDEX IF NOT EXISTS idx_artifacts_checksum_md5 ON artifacts(checksum_md5) WHERE checksum_md5 IS NOT NULL;
+CREATE INDEX IF NOT EXISTS idx_artifacts_checksum_sha1 ON artifacts(checksum_sha1) WHERE checksum_sha1 IS NOT NULL;