fix(rcart): use defaultCryptoAmount for Transak widget

Transak rejects `cryptoAmount` when combined with fiatCurrency params.
Use `defaultCryptoAmount` which pre-fills the amount without conflicting.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/rcart/mod.ts

@@ -1773,7 +1773,7 @@ routes.post("/api/payments/:id/transak-session", async (c) => {
 		defaultCryptoCurrency: p.token,
 		walletAddress: p.recipientAddress,
 		disableWalletAddressForm: 'true',
-		cryptoAmount: effectiveAmount,
+		defaultCryptoAmount: effectiveAmount,
 		partnerOrderId: `pay-${paymentId}`,
 		email,
 		themeColor: '6366f1',