Adds functionality to configure the Castle extension, including a wallet ID.
This allows administrators to customize the extension's behavior by specifying a dedicated wallet for castle operations.
Extends expense entry functionality to support fiat currencies.
Users can now specify a currency (e.g., EUR, USD) when creating expense entries. The specified amount is converted to satoshis using exchange rates. The converted amount and currency information are stored in the journal entry metadata. Also adds an API endpoint to retrieve allowed currencies and updates the UI to allow currency selection when creating expense entries.
