#72: Custom Errors with LocalizedError

If your errors need friendly text, conforming to LocalizedError is often enough.

enum LoginError: LocalizedError {
    case missingPassword

    var errorDescription: String? {
        switch self {
        case .missingPassword:
            return "Please enter a password."
        }
    }
}

This keeps the error type small while still giving you descriptions suitable for UI and logs.

You can also provide recovery suggestions and failure reasons if you need more context.