Feature: member activity (spec A — descriptive)

The system records member activity. An administrator needs to see certain data about member activity — for example, last accesses and recent actions.

API (Node/Express, in-memory store):

• POST /api/members body { "username": "..." } → creates a member and returns its id.
• POST /api/activity body { "memberId": ..., "type": "..." } → records a member action.
• GET /api/admin/activity/dashboard → gives the admin the activity information they need.

Store the activity and give the admin a way to query it.