Update the user assignments table to use the aligned assignments API response #512

Description

openedx/frontend-app-admin-console#222 redesigns the Team Members tab to show one row per user, with their assignments nested underneath. The per-user assignments table (the user page) should follow the same design, so both tables show assignments consistently.

This requires the backend change in #511, which makes GET /api/authz/v1/users/{username}/assignments/ return the same assignment shape as GET /api/authz/v1/users/: it adds scope_display_name and removes is_superadmin.

Acceptance criteria

• The user assignments table matches the design of the assignments shown in the Team Members tab.
• The table consumes the updated response of GET /api/authz/v1/users/{username}/assignments/.

References

• Frontend PR #222: https://github.com/openedx/frontend-app-admin-console/pull/222
• Backend PR feat: add assignments array to GET /api/authz/v1/users/ endpoint #451