Update H5P.Core to v1.28

Upgrade H5P.Core to version 1.28 to restore compatibility with H5P.com and ensure smoother interoperability between platforms. This update will align Lumi with the current H5P standard, reduce integration issues, and improve reliability when importing, exporting, or sharing content. The goal is to maintain compatibility with the wider H5P ecosystem and keep the platform technically up to date.