Fixed: customer imports show clear row errors

Customer import reports now explain skipped rows with clear messages. Contact conflicts remain actionable, while unexpected failures ask you to try again later without showing internal technical details. Imports also reuse your custom-field settings throughout each file, reducing repeated lookups while keeping field validation and existing customer details intact. Re-importing equivalent custom-field values now keeps rows unchanged, and rejected choices or invalid statuses no longer count as updates. Imports also spend less time preparing updates for your connected integrations, reducing the wait for the final report while preserving existing notification handling.