feat: add xBull wallet adapter

[gloriaelishahabu]

Overview

xBull is one of the most widely used Stellar wallets on mobile and desktop. This issue tracks adding xBull support to WalletConnect and StellarPayProvider.

What needs to be built

• Research xBull Wallet SDK (@creit-tech/xbull-wallet-connect)
• Implement connectXBull() adapter in StellarPayProvider.tsx
• Implement signWithXBull() for transaction signing
• Handle the xBull iframe-based connection flow
• Test on testnet

xBull SDK reference

import { xBullWalletConnect } from "@creit-tech/xbull-wallet-connect";

const wallet = new xBullWalletConnect();
await wallet.connect();
const { publicKey } = await wallet.getPublicKey();
const { signedXDR } = await wallet.sign({ xdr: unsignedXdr, network: "TESTNET" });

Acceptance criteria

• <WalletConnect wallets={["xbull"]} /> works end to end
• Signing works through useTransaction
• Works on both mobile and desktop browsers

Notes

xBull uses an iframe bridge so the connection flow is slightly different from Freighter. May need a wrapper component to handle the iframe lifecycle.