chore: add pre-commit ruff hook with auto-fix

- scripts/hooks/pre-commit: runs ruff --fix for root and web/ (matching CI)
  and re-stages any auto-fixed files so they land in the commit
- Makefile: add install-hooks target (run once after clone)
- pyproject.toml: exclude web/ from root ruff (web has its own config)
- Fix remaining import sort warnings caught by the new hook

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

web/tests/test_billing_webhooks.py

@@ -5,13 +5,12 @@ Covers signature verification, event parsing, subscription lifecycle transitions
 import json
 
 import pytest
+from beanflows.billing.routes import get_billing_customer, get_subscription
 from conftest import make_webhook_payload, sign_payload
 from hypothesis import HealthCheck, given
 from hypothesis import settings as h_settings
 from hypothesis import strategies as st
 
-from beanflows.billing.routes import get_billing_customer, get_subscription
-
 WEBHOOK_PATH = "/billing/webhook/paddle"
 SIG_HEADER = "Paddle-Signature"