chore: .gitignore에 ari.db 부속 파일(-shm/-wal·루트) 추가

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -17,7 +17,8 @@ backend/.venv/
 backend/__pycache__/
 backend/**/__pycache__/
 backend/.env
-backend/ari.db
+backend/ari.db*
+ari.db*
 backend/.pytest_cache/
 backend/.ruff_cache/
 *.pyc