Describe the bug

As part of opencloud-eu/web#2171 and #2454, favorites were enabled in OpenCloud.

While the backend already supports marking (project) spaces as favorites, this state is currently not reflected in the Graph API.

To properly support favorite spaces in the web app, we need to introduce a custom “favorite” flag on the relevant drive endpoints so that the frontend can correctly read and display the favorite status.

fyi @aduffeck