Returned by GET /api/community/feed to CommunityFeedProvider, which
asks again as the socket tells of changes, and rendered by the
CommunityFeed component with who is online, which the client knows from
its socket. community-service.ts gathers it. Everything in it is public:
every reader gets the same feed.
The latest events, newest first, 12 at most.
week:
The last week's figures, as /community shows them: as of the server's
last refresh.