Pay Multiple Invoices

Pay multiple invoices with multiple succeeded payment intents. Use case: Batch payment processing for multiple subscriptions created in a single checkout. This endpoint is called by the checkout flow after payment intents are confirmed. Requirements: - All payment_intent_ids must be in SUCCEEDED status - All payment intents must belong to the same customer - All invoices must use the same currency Behavior: - Matches payment intents to invoices (exact amount first, then sorted) - Marks each invoice as PAID using its corresponding processor attempt - Activates subscriptions linked to paid invoices (INCOMPLETE → ACTIVE) - Handles partial failures gracefully (continues processing remaining invoices) Returns detailed outcome for each invoice including: - Invoice status and ID - Subscription status and ID (if applicable) - Processor attempt details - Success/failure status with error messages