List all member assignments

$curl https://novapai.ai/api/v1/guardrails/assignments/members \
>-H "Authorization: Bearer <token>"

{
  "data": [
    {
      "id": "550e8400-e29b-41d4-a716-446655440000",
      "user_id": "user_abc123",
      "organization_id": "org_xyz789",
      "guardrail_id": "550e8400-e29b-41d4-a716-446655440001",
      "assigned_by": "user_abc123",
      "created_at": "2025-08-24T10:30:00Z"
    }
  ],
  "total_count": 10
}