fix(request-pickup): allow positive COD payout deficits

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Summary

• allow COD deficit rows to remain selectable for request pickup when their effective COD payout is non-negative
• calculate pickup eligibility from WC total minus discounted shipping, insurance, and COD fee instead of blocking on the stale deficit flag alone
• keep deficit rows blocked when the effective payout is still negative

Why

Some orders are flagged as deficit because the stored minimum/deficit calculation used raw values, but the actual effective COD payout can still be positive after shipping discounts. Those orders should be processable in the request pickup checklist instead of being disabled only because is_deficit is set.

Validation

• rtk vendor/bin/paratest --configuration paratest.xml --filter RequestPickupPaymentFlowTest
• rtk make zip