Extract the events list UNION query out of EventsController #2937

Problem

EventsController builds the paginated upcoming/past events listing inside the controller: paginated_events (~80 lines) constructs a raw Arel UNION ALL across workshops, meetings, and events, plus a separate COUNT query and manual Pagy wiring, and load_events re-hydrates AR objects from the returned id/type pairs. fetch_upcoming_events and fetch_past_events are also near-duplicates of each other.

This is query logic, not HTTP coordination, and it makes the controller the largest non-admin one in the app. The repo already has app/queries/ (DashboardQuery, SponsorsSearch) — this work belongs there.

Proposed change

• Move the UNION ALL construction, count, pagination, and re-hydration into a single query class, e.g. app/queries/events_feed_query.rb, with an upcoming: flag so fetch_upcoming_events / fetch_past_events collapse into one method.
• Controller keeps only: parse params[:page], call the query, assign for the view.

Acceptance

• EventsController#upcoming / #past are a few lines each and contain no Arel.
• Existing behaviour unchanged: same ordering, grouping by date, 20 rows/page, DB-level count and pagination.
• bundle exec rspec spec/controllers/events_controller_spec.rb (and the feature specs touching the events pages) pass.