Add integration tests for deduplication and ref_count

- Add test_integration_uploads.py with 12 tests for duplicate upload scenarios
- Add test_ref_count.py with 7 tests for ref_count management
- Fix ArtifactDetailResponse to include sha256 and checksum fields
- Fix health check SQL warning by wrapping in text()
- Update tests to use unique content per test run for idempotency

backend/app/routes.py

@@ -13,7 +13,7 @@ from fastapi import (
 )
 from fastapi.responses import StreamingResponse, RedirectResponse
 from sqlalchemy.orm import Session
-from sqlalchemy import or_, func
+from sqlalchemy import or_, func, text
 from typing import List, Optional, Literal
 import math
 import re
@@ -263,7 +263,7 @@ def health_check(
 
     # Check database connectivity
     try:
-        db.execute("SELECT 1")
+        db.execute(text("SELECT 1"))
         database_healthy = True
     except Exception as e:
         logger.warning(f"Database health check failed: {e}")
@@ -2131,9 +2131,13 @@ def get_artifact(artifact_id: str, db: Session = Depends(get_db)):
 
     return ArtifactDetailResponse(
         id=artifact.id,
+        sha256=artifact.id,  # SHA256 hash is the artifact ID
         size=artifact.size,
         content_type=artifact.content_type,
         original_name=artifact.original_name,
+        checksum_md5=artifact.checksum_md5,
+        checksum_sha1=artifact.checksum_sha1,
+        s3_etag=artifact.s3_etag,
         created_at=artifact.created_at,
         created_by=artifact.created_by,
         ref_count=artifact.ref_count,