Attach org user to team

Users who own teams should be able to add org users to a team.

Note: it should be expected that a team owner can add users of future roles.

The issue names no files, tests, or entry points. Start by locating the team-membership and role-authorization paths in the TypeScript/GraphQL application, then inspect existing team-user behavior and tests. Done means team owners can add organization users, including users with roles introduced later, with coverage for the permission boundary.

Written by the indexing model from the issue text.