Cap or paginate the workshop list in DashboardQuery.upcoming_events_for_user #3093

DashboardQuery.upcoming_events_for_user loads every upcoming workshop from the member's chapters, with no limit and no pagination:

def self.chapter_workshops_for(member)
  Workshop.upcoming
          .eager_load(:chapter, :sponsors, :organisers, :permissions)
          .preload(workshop_host: :sponsor)
          .where(chapter: member.chapters)
          .to_a
end

The homepage query in the same class caps at MAX_WORKSHOP_QUERY = 10 (upcoming_workshops), and /dashboard renders every card it receives (app/views/dashboard/dashboard.html.haml renders EventCardComponent.with_collection for each date group).

Exposure today

Measured against the local production snapshot (codebar_production_dump):

• busiest chapter runs 5 workshops in a month, p95 = 2
• one member belongs to 40 chapters, but no member has more than 5 upcoming workshop cards
• 54 chapters exist, 4 have upcoming workshops in the snapshot

So no member is affected right now. The risk is a member subscribed to several busy chapters as workshop volume grows, or a chapter that starts scheduling further ahead.

Options

• cap the chapter-workshops branch at MAX_WORKSHOP_QUERY, matching the homepage query
• paginate the dashboard card list

A cap changes what members see, so this needs a product decision rather than a pure refactor.

Found while reviewing #3074. The query existed before that PR and moved unchanged, so this predates it.