fix(pos-payment-overpay-fix): pOS selfpay: payments exceed total

work/artifacts/POS-PAYMENT-OVERPAY-FIX/implementer.md

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+# Implementer — POS-PAYMENT-OVERPAY-FIX
+
+## Changes
+- Frontend (terminal page): clamp `amountCents` to `Math.min(remainingCents, totals.total)` to avoid 1-cent overpayment
+- Backend (create-pos-sale): allow 1-cent tolerance in payment overpayment validation to absorb rounding diffs between frontend cached prices and backend canonical total
+
+## Validation
+- `cd project && npm run build` ✅
+- `cd project/apps/pos && npm run build` ✅