## Summary
Adds the Nigerian Naira (NGN, ₦) as a selectable currency.
Conversion support required no code change: rates come from the
fawazahmed0 currency-api CDN, which already serves NGN (verified live,
e.g. `EUR→NGN ≈ 1566.8`). `ExchangeRateService` /
`CurrencyConversionService` are currency-agnostic, so NGN converts as
soon as it's a valid option.
## Changes
- `config/currencies.php` — add NGN entry (allowed as both primary and
account currency).
- `resources/js/utils/currency.ts` — add `₦` to the symbol map.
- `lang/es.json` — Spanish translation for the currency name.
- `tests/Feature/CurrencyOptionsTest.php` — assert NGN is exposed as a
primary and account currency.
## Testing
- `php artisan test tests/Feature/CurrencyOptionsTest.php
tests/Feature/CurrencyConversionServiceTest.php
tests/Feature/LocalizationTest.php` — pass
- `vendor/bin/pint`, `bun run format`, `bun run lint`, `vitest run
currency.test.ts` — pass
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