Stage 3 Task 3.1. Add frozen_by_balance_at guard in chargeForDelivery() before
bcmath arithmetic. Even if balance_rub > 0, a tenant flagged by
BalancePreflightSweepJob must not be charged for new lead deliveries. The
InsufficientBalanceException throw triggers the existing auto-pause flow
(RouteSupplierLeadJob::handleInsufficientBalance → projects.is_active=false +
ZeroBalancePausedMail rate-limited). Spec §4.3.1.
Дмитрий