Release v7.5.1

Changed

• The documentation rules now spell out how to link to another product's page: use its root-relative site route (/arc/backend/csharp/embedded-event-model/), not an absolute cratis.io or GitHub blob/ URL that the site build never checks
• The documentation rules state that DocFX xref: symbol links are not supported: the site converts them to plain text, so link to the page that documents the type instead
• The documentation rules explain how a product's own link gate should skip site-absolute links by rule rather than by product name, so a product's internal links stay checked