fix: apply black formatting to react_agent_service.py

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ChingEnLin

backend/services/react_agent_service.py

@@ -21,7 +21,6 @@
 from services.gemini_service import extract_python_code
 from services.mongo_service import execute_mongo_query, transform_mongo_result
 
-
 WRITE_METHODS = {
     "insert_one",
     "insert_many",