users_count on UserGroup does not include users assigned via primary_group

[Rike-cz]

The users_count relation on UserGroup is defined as a belongsToMany count against the users_groups pivot table:

'users_count' => [
    User::class,
    'table' => 'users_groups',
    'count' => true
]

However, the primary_group relationship is a separate belongsTo using a primary_group_id foreign key stored directly on the users table. As a result, users whose only group membership is through primary_group_id — which includes every user created through the default registration flow — are not counted in the users_count column displayed in the backend UserGroups list.