[DwC export]: Provide link to GBIF data validator in export workflow

[grantfitzsimmons]

Goal

After a successful export, provide the user with a direct link to the GBIF data validator so they can externally verify their DwCA. This can be done in a dialog, and it should simply say:

"Export successful! If you have not already, you can validate the exported data set using the GBIF Data Validator"

Background

External validation gives users confidence their export is standards-compliant before publishing to GBIF or other aggregators.

Acceptance Criteria

• After a successful DwCA download or export run, a notification or result dialog includes a Validate on GBIF link.
• The link opens https://www.gbif.org/tools/data-validator in a new browser tab.
• The link is accompanied by brief instructional text (e.g., "Upload your downloaded archive to check for errors.").