Cloud client errors

@tekmemo/cloud-client should expose typed errors for auth, validation, rate limits, network failures, and server errors.

import { isTekMemoCloudError } from "@tekmemo/cloud-client";

try {
  await client.memory.readCore();
} catch (error) {
  if (isTekMemoCloudError(error)) {
    console.error(error.code, error.status);
  }
}

Error messages should redact common secret patterns such as tk_live_..., Bearer ..., and provider keys.