feat: typed error handling for wallet hooks (#44)

[satoshai-dev]

Summary

Adds wagmi-style typed error classes for all wallet hooks, replacing plain Error throws:

• BaseError — base class with shortMessage, details, and walk() for cause chain traversal
• WalletNotConnectedError — thrown when calling a hook without an active connection
• WalletNotFoundError — thrown when wallet extension is not installed (OKX)
• UnsupportedMethodError — thrown for unsupported wallet methods (e.g. OKX + stx_signStructuredMessage), exposes method and wallet
• WalletRequestError — wraps wallet RPC failures with method, wallet, and original cause

Each error exports a *ErrorType for TypeScript discriminated unions via error.name.

Developer experience

const { error } = useSignStructuredMessage()

if (error instanceof UnsupportedMethodError) {
  toast(`${error.wallet} doesn't support ${error.method}`)
}

// Or via name discrimination
if (error?.name === 'WalletRequestError') {
  console.log(error.method, error.wallet, error.cause)
}

Closes #44

Files changed

• New: packages/kit/src/errors.ts — error class definitions
• Modified: 5 hooks — useSignMessage, useSignStructuredMessage, useSignTransaction, useTransferSTX, useWriteContract
• Modified: packages/kit/src/index.ts — exports all error classes and types
• Modified: 4 test files — updated assertions to use shortMessage

Test plan

• All 144 tests pass
• Build, lint, typecheck pass

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