fix(grant): resolve repo by name via the singular `repo` field (COR-699)

The control plane returns a name-filtered repo list under the singular repo field (like org/project), not the plural repos array — repos is only populated for an unfiltered page. resolveRepoRef read repos, so grant repo {list,add,remove} <name> --project <p> always 404'd with "no repo named" even when the repo existed. The fixture mocked the plural array too, hiding it; it now mirrors the real server's singular field.