fix: drop chat_plan_upgrade from refundable types

The mid-cycle chat upgrade path inserts chat_plan_upgrade without a
Stripe invoice or payment intent id, so a refunded upgrade charge could
never be resolved back to it. Keep only the flows that persist an
invoice id (chat_plan_start, chat_plan_renewal) refundable.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: steebchen

apps/api/src/stripe.ts

@@ -2669,14 +2669,17 @@ export async function handleChargeRefunded(
 		return;
 	}
 
+	// chat_plan_upgrade is intentionally omitted: the mid-cycle upgrade path in
+	// routes/chat-plans.ts inserts that transaction without a stripeInvoiceId or
+	// stripePaymentIntentId, so a refunded upgrade charge could never be resolved
+	// back to it here. Add it only once that insert persists the Stripe ids.
 	const refundableTypes: (
 		| "credit_topup"
 		| "dev_plan_start"
 		| "dev_plan_renewal"
 		| "dev_plan_upgrade"
 		| "chat_plan_start"
 		| "chat_plan_renewal"
-		| "chat_plan_upgrade"
 		| "subscription_start"
 	)[] = [
 		"credit_topup",
@@ -2685,7 +2688,6 @@ export async function handleChargeRefunded(
 		"dev_plan_upgrade",
 		"chat_plan_start",
 		"chat_plan_renewal",
-		"chat_plan_upgrade",
 		"subscription_start",
 	];