Add admin authentication for community member listing

[Lakes41]

The admin member listing service includes a TODO to ensure the requester is an admin. Implement authentication and authorisation for GET /v1/communities/:communityId/members so member data is not exposed publicly.

Suggested tasks

• Define the authentication mechanism for admin API access
• Check that the requester has an active admin role for the community
• Return 401 for unauthenticated requests
• Return 403 for authenticated users without admin access
• Add tests for admin, non-admin, and unauthenticated access
• Document the required headers or auth flow

Acceptance criteria

• Community member listing requires admin access
• Non-admin users cannot list community members
• Authentication and authorisation failures return clear responses
• Tests cover allowed and denied cases

[Adesam007-pr3dator]

Hi, I would love to work on this issue