Create consolidated error code reference catalog

Problem

Error codes and types are scattered across multiple files. There's no single reference for all possible errors and how to handle them.

Current State

Errors defined in:

• src/agent/errors.ts
• src/protocol/rpc.ts
• Various other modules

Impact

• Developers can't easily find all error types
• No guidance on error recovery strategies
• Difficult to build comprehensive error handling

Recommendation

Create docs/errors.md with:

1. Complete Error Catalog

2. Error Hierarchy Diagram

3. Code Examples

try {
  await wallet.sendUSDC(to, amount);
} catch (error) {
  if (error instanceof InsufficientFundsError) {
    // Handle insufficient funds
  } else if (error instanceof RPCRequestError) {
    // Handle RPC issues
  }
}

Priority

Medium - Developer experience

Start by reading src/agent/errors.ts and src/protocol/rpc.ts, then inspect the other error-defining modules to identify the complete set of codes and types. Create docs/errors.md with the catalog, recovery guidance, hierarchy diagram, and TypeScript handling examples; done means developers have one reference covering all identified errors.