[bug] - Fix btc price and currency conversion on transaction history

[islandbitcoin]

Fixes lnflash/flash-mobile#547

[linear]

ENG-26

[brh28]

@Nodirbek75 @islandbitcoin Which graphql query is this? What field are we referencing? A sample query would be best

[chengyixu]

Proposing to fix BTC price and currency conversion on transaction history.

Root Cause (linking to the mobile-side fix in flash-mobile #547):
The transaction history in the mobile app re-computes JMD amounts using the current BTC price rather than the settlement price. This means every BTC transaction shows a different JMD amount each time the BTC price moves — making historical data unreliable.

Fix approach:

1. Use settlementDisplayAmount / settlementDisplayCurrency already returned by the Flash GraphQL API — these fields contain the correct JMD amount locked in at settlement time. The API already has the right data; the mobile just needs to use it.

2. In TxItem.tsx (the transaction list component): replace the live-price reconversion with tx.settlementDisplayAmount for display. The detail screen already does this correctly — sync the list behavior.

3. For USD wallet transactions: remove the * 100 multiplication (settlementAmount is already in cents).

4. For Breez SDK transactions in useBreezPayments.ts: use the user's actual displayCurrency instead of hardcoded 'USD'.

This is the mobile side of the full fix coordinated with backend #282 and #284.

Timeline: Mobile fix within 48 hours. Ready to start immediately.