Introduce a mechanism to track and audit changes in exchange rates.
This includes:
- Creating `ExchangeRateHistory` model and migration to store rate changes.
- Implementing `ExchangeRateService` to encapsulate rate logic.
- Updating `UpdateExchangeRates` command to record history when rates change.
- Adding `ExchangeRateHistoryResource` to the Filament admin panel for monitoring.
