Load Shape - Downloadable validation report

As a measure developer, I want to download the validation report in a portable format (CSV, Excel, text, or PDF), so that I can document issues, share errors with stakeholders, and track corrections across multiple upload attempts.

Acceptance Criteria:

• A download button is available on the validation results page

• Supported formats include at least one of: CSV, Excel (.xlsx)

• The downloaded file includes all validation errors shown on screen

• The filename reflects the upload session

• The download is available immediately after validation completes and does not require re-running the validation