chore(backend): add black/isort/flake8 + pre-commit

backend/scripts/lint.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+. .venv/bin/activate
+
+python -m black .
+python -m isort .
+python -m flake8 .