docs: add author to MR-VPP PUM v1

Align the PUM frontmatter with the ATBD, which already credits the
European Environment Agency as author.

Author: MatMatt

DOCS/MRVPP/MRVPP_PUM_v1/MRVPP_PUM_v1.qmd

@@ -3,6 +3,7 @@ title: 'Medium Resolution Vegetation Phenology and Productivity (MR-VPP) – Pro
 subtitle: 'Copernicus Land Monitoring Service'
 category: products
 date: '2026-06-18'
+author: 'European Environment Agency (EEA)'
 ---
 
 Reference Document for **Version 5.0 Issue 2.0**