GitLab

The response interceptor in client.ts transforms errors into plain
objects {status, code, message}, but catch blocks were checking
error.response?.status (AxiosError format) which never matched.

- Add error field passthrough in client.ts interceptor
- Refactor BulkEditAccountModal to use pre-check API (checkMixedChannelRisk)
  before submit, matching the single edit flow
- Fix EditAccountModal catch blocks to use interceptor error format
- Add bulk-update mixed channel unit tests