feat: Add localized number formatting for different fiat currencies

[AlAfiz]

Description

Our utility currently formats all balances in US Dollars ($).
As we prepare for a global user base, we need our formatter to support different locales (like Euros or GBP).
We need to update our numberFormat utility to accept an optional currency string and format it accordingly.
This makes the platform instantly more accessible to non-US users.

Requirements

• Update the formatToUSD utility function and rename it to formatCurrency(amount, currencyCode).
• Default the currencyCode parameter to 'USD'.
• Use Intl.NumberFormat with the dynamic currency code.
• Test the function by displaying one dummy metric on the dashboard in Euros (EUR).