Sample data imports without access errors

Every time a portal synced the MeshWeaver sample content, the import finished with errors and the log filled with dozens of refused access grants. The sample data shipped access assignments that gave named demo users edit rights on a space the repository owns — a combination the mesh refuses by design, because a space kept in sync with a repository is rewritten on every sync and only the sync itself may change it.

The sample grants are now read-only, so the import completes cleanly and its status reads "Imported" instead of "Imported with errors". Three grants that named a role which does not exist now name a real one, so the group hub they were meant to serve actually gets the read access it was always supposed to have.

Nothing changes for anyone's real access. Administrator rights on the demo spaces were only ever meaningful on a developer's own machine, and are now configured there the same way every other deployment configures them.