feat: SorobanContractInvoker component and useContractCall hook

[gloriaelishahabu]

Overview

Soroban smart contracts are the future of Stellar dApps. This issue tracks adding a useContractCall hook and SorobanContractInvoker component that lets dApps invoke Soroban contract functions through the same wallet adapter layer already in StellarPayProvider.

What needs to be built

• useContractCall(contractId, method, args) hook using SorobanRpc.Server
• Handle simulation → authorization → submission lifecycle
• SorobanContractInvoker component for no-code contract invocation UI
• Support for reading contract state (view functions — no signing needed)
• Export from barrel

API shape

const {
  invoke,     // (args: xdr.ScVal[]) => Promise<SorobanRpc.GetTransactionResponse>
  simulate,   // (args: xdr.ScVal[]) => Promise<SorobanRpc.SimulateTransactionResponse>
  result,     // SorobanRpc.GetTransactionResponse | null
  status,     // "idle" | "simulating" | "signing" | "submitting" | "success" | "error"
  error,      // string | null
} = useContractCall(contractId, "transfer");

Why this matters

• StellarBridge and other Wave projects use Soroban contracts
• No existing React library abstracts the simulate → sign → submit → poll lifecycle
• This makes stellar-pay-ui useful beyond just payments — it becomes the standard Soroban UI toolkit

References

• Soroban RPC docs
• stellar-sdk SorobanRpc