User activation funnel metrics

curl --request GET \
  --url https://api.example.com/api/admin/activation-stats \
  --header 'Authorization: Bearer <token>'

{
  "total_users": 123,
  "activated_users": 123,
  "activation_rate_pct": 123,
  "activated": [
    {
      "user_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "email": "<string>",
      "activated_at": "2023-11-07T05:31:56Z",
      "activation_memory_count": 123,
      "activation_recall_count": 123,
      "activation_session_count": 123
    }
  ]
}