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/services/webhooks.py

@@ -14,6 +14,7 @@ from finance.models import Invoice, Payment, UserSubscription
 from finance.services.plans import (
     assign_plan_from_stripe,
     get_or_create_user_subscription,
+    log_subscription_auth_event,
     resolve_plan_from_stripe_price,
 )
 
@@ -421,6 +422,7 @@ def handle_customer_subscription_deleted(subscription: dict[str, Any]):
         return None
 
     sub = get_or_create_user_subscription(user)
+    prev_status = sub.status
     sub.status = UserSubscription.Status.CANCELED
     sub.cancel_at_period_end = False
     sub.current_period_end = _ts_to_dt(subscription.get("current_period_end"))
@@ -430,6 +432,16 @@ def handle_customer_subscription_deleted(subscription: dict[str, Any]):
     if sub.source == UserSubscription.Source.NONE:
         sub.source = UserSubscription.Source.STRIPE
     sub.save()
+    if prev_status != UserSubscription.Status.CANCELED:
+        log_subscription_auth_event(
+            user,
+            started=False,
+            detail=(
+                f"plan={sub.plan.slug if sub.plan_id else 'none'} "
+                f"source={sub.source} status={sub.status} "
+                f"stripe_subscription_id={sub.stripe_subscription_id}"
+            ),
+        )
     return sub