getAvailableBuyProviderTypes() now returns [moonpay] only when moonPayApiKey is
non-empty, so MoonPay's Buy button appears only in builds where the CI secret is
present (and the exchange-helper signer is live). Both build workflows now inject
MOONPAY_API_KEY -> moonPayApiKey and EXCHANGE_HELPER_API_KEY -> exchangeHelperApiKey
alongside Trocador + WalletConnect. moonPaySecretKey is server-side and never injected.