chore: fix all ruff lint warnings (unused imports, unsorted imports, unused vars)

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

web/tests/test_billing_helpers.py

@@ -7,7 +7,6 @@ from hypothesis import settings as h_settings
 from hypothesis import strategies as st
 
 from beanflows.billing.routes import (
-
     can_access_feature,
     get_billing_customer,
     get_subscription,
@@ -66,7 +65,7 @@ class TestUpsertSubscription:
             status="active",
             provider_subscription_id="sub_same",
         )
-        returned_id = await upsert_subscription(
+        await upsert_subscription(
             user_id=test_user["id"],
             plan="pro",
             status="active",