Better currency visibility in checkout

We've updated how currency information appears across the checkout form so supporters can easily confirm they're donating in the correct currency.

When the donation currency differs from a supporter's location currency and the currency symbol is not unique (like $ used for multiple currencies), we now add the ISO code throughout the checkout form. For example, a supporter in Canada donating in US dollars will see "$100 USD" instead of just "$100" at every step, clarifying that amounts are in US dollars, not Canadian dollars.

When the donation currency matches the supporter's location currency, we show the full currency name next to the total amount on the payment screen. For example, a supporter in Canada donating in Canadian dollars will see "$100 CAD" next to the total, so they can verify the currency at the most critical step before completing their donation.

We've also updated how currency symbols appear in amount fields. The symbol position now matches regional conventions for each currency. For example, US dollars ($) appear on the left as $100, while euros (€) appear on the right as 100€. This creates a more familiar experience for supporters across different regions.