No refund/chargeback clawback for manual payouts already marked paid

[guillermoscript]

Part of #493 (Phase 2 — payout money-accuracy).

Problem

markPayoutPaid is a one-way ratchet — once a payout is recorded, nothing re-checks whether the underlying transactions it was based on later flip to refunded/failed. If a PayPal sale gets refunded after you've already paid the school their share, /platform/payouts has no way to reflect that you're now effectively owed money back — it'll just show $0 owed going forward for that tenant, silently absorbing the loss with no record of it.

Wanted

When computing netOwed in computeOwedBalances, subtract refunded-transaction amounts (scaled by the split, same as any other transaction) from grossCollected/grossOwed, so a refund after payout is reflected as a negative adjustment on the next payout cycle rather than disappearing. Surface it in the UI (e.g. a "clawback" line) rather than silently netting it into netOwed.

Acceptance

• A refund on a transaction that was already included in a paid-out payout reduces what's owed on the next cycle.
• The clawback is visible on the payouts page, not just silently absorbed into the running total.
• Unit test: transaction refunded after being paid out → next computeOwedBalances call reflects the clawback.

[guillermoscript]

An AI agent is picking this up as part of epic #493's Phase 2 follow-through.

Fixed in PR #506: transactions with status = 'refunded' are now included in the payouts-owed calculation instead of being excluded from the query entirely. Their scaled amount (using the same split-percentage logic as any other transaction) is surfaced as a distinct clawback figure on /platform/payouts, both in a per-currency banner and a per-row column, and it reduces netOwed on the next cycle rather than silently vanishing.

Unit tests cover: refund-after-payout produces a visible clawback and reduces netOwed; clawback is reported even with nothing else outstanding; a refund in one currency doesn't clawback a balance in another; clawback uses the transaction's own snapshotted split (issue #496 semantics), not the tenant's current one.

[guillermoscript]

Closed by #506, merged into master.

Refunded transactions no longer silently vanish from the payout calculation — they're now included, scaled by the split, and surfaced as a distinct clawback figure that reduces netOwed on the next cycle. Visible both in a per-currency banner and a per-row column on /platform/payouts. Full test record and live-verification screenshot are on the PR.