refactor: update database.py to use new config module

Update import statement from app.core.config to config.settings as part
of YAML configuration migration.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/core/database.py

@@ -3,7 +3,7 @@ from typing import Generator
 from sqlalchemy import create_engine
 from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker
 
-from app.core.config import settings
+from config.settings import settings
 
 engine = create_engine(
     settings.database_url,