Feature: member activity (spec B — prescriptive)

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

• POST /api/members body { "username": "..." } → 201 { "member": { "id": ..., "username": "..." } }.
• POST /api/activity body { "memberId": ..., "type": "..." } → 201. type is a free string (login, post, comment, share, …) — the list is illustrative, NOT exhaustive: any type must be recorded and counted with no code changes.
• GET /api/admin/activity/dashboard → 200, with this exact shape:

  { "perMember": [ { "memberId": ..., "lastAccess": "<ISO>", "actionsByType": { "<type>": <count> } } ],
    "activeMembers7d": <int> }
  

UC-1 — Aggregated per-member view

For each member, actionsByType is the AGGREGATED count by type of their actions (NOT raw rows); lastAccess = ISO timestamp of their last action. (Postcondition: if a member did post twice, actionsByType.post == 2.)

UC-2 — Active members

activeMembers7d = number of members with ≥1 action in the last 7 days.

Acceptance criterion

A type outside the illustrative list (e.g. share) must appear aggregated in actionsByType with no special handling. The dashboard returns aggregates, never the raw log.