Log account delete and subscription changes in UserAuthEvent

Add account_deleted, subscription_started, and subscription_updated
event types. Soft-delete, Checkout/Backer assign, and Stripe portal
lifecycle webhooks write audit rows visible on the user admin.

llm_be/finance/tests/test_webhooks.py

@@ -8,6 +8,7 @@ from rest_framework import status
 from rest_framework.test import APITestCase
 
 from chat_backend.tests.factories import make_company, make_user
+from chat_backend.models import UserAuthEvent
 from finance.models import Invoice, Payment, UserSubscription
 from finance.services.plans import assign_plan_from_stripe, seed_subscription_plans
 from finance.services.webhooks import (
@@ -123,10 +124,15 @@ class WebhookHandlerUnitTestCase(APITestCase):
             "currency": "usd",
         }
         handle_checkout_session_completed(session)
-        sub = self.user.subscription
+        sub = UserSubscription.objects.get(user=self.user)
         self.assertEqual(sub.plan.slug, "founders")
         self.assertEqual(sub.source, UserSubscription.Source.STRIPE)
         self.assertEqual(sub.status, UserSubscription.Status.ACTIVE)
+        started = UserAuthEvent.objects.get(
+            user=self.user,
+            event_type=UserAuthEvent.EventType.SUBSCRIPTION_STARTED,
+        )
+        self.assertIn("founders", started.detail)
 
     def test_subscription_updated_sets_cancel_at_period_end(self):
         seed_subscription_plans(update_existing=False)
@@ -149,6 +155,11 @@ class WebhookHandlerUnitTestCase(APITestCase):
         self.assertTrue(sub.cancel_at_period_end)
         self.assertEqual(sub.status, UserSubscription.Status.ACTIVE)
         self.assertIsNotNone(sub.current_period_end)
+        updated = UserAuthEvent.objects.filter(
+            user=self.user,
+            event_type=UserAuthEvent.EventType.SUBSCRIPTION_UPDATED,
+        ).latest("created")
+        self.assertIn("cancel_at_period_end=True", updated.detail)
 
     def test_subscription_deleted_marks_canceled(self):
         seed_subscription_plans(update_existing=False)
@@ -169,6 +180,11 @@ class WebhookHandlerUnitTestCase(APITestCase):
         sub = UserSubscription.objects.get(user=self.user)
         self.assertEqual(sub.status, UserSubscription.Status.CANCELED)
         self.assertFalse(sub.cancel_at_period_end)
+        updated = UserAuthEvent.objects.filter(
+            user=self.user,
+            event_type=UserAuthEvent.EventType.SUBSCRIPTION_UPDATED,
+        ).latest("created")
+        self.assertIn("status=canceled", updated.detail)
 
 
 class StripeWebhookViewTestCase(APITestCase):