fix: eager load organisers on homepage events

[mroderick]

Summary

• Add eager loading for :organisers association on Workshop, Meeting, and Event queries in DashboardController#upcoming_events and upcoming_events_for_user

Analysis

The homepage (DashboardController#show) was causing N+1 queries when rendering events because:

1. Workshops - Query included :chapter and :sponsors but not :organisers
2. Meetings - Query only included :venue
3. Events - Query included :venue and :sponsors but not :organisers

When rendering _event.html.haml, the view accesses event.organisers which triggered a separate database query for each event.

Fix

Added :organisers to the .includes() calls for all three event types:

workshops = Workshop.upcoming.includes(:chapter, :sponsors, :organisers)
meeting = Meeting.includes(:venue, :organisers).next
events = Event.includes(:venue, :sponsors, :organisers).upcoming.take(...)

Verification

SQL proof: With :organisers included, ActiveRecord generates a single query with LEFT OUTER JOINs to fetch permissions and members:

LEFT OUTER JOIN "permissions" ON "permissions"."resource_type" = 'Workshop' 
  AND "permissions"."resource_id" = "workshops"."id"
LEFT OUTER JOIN "members_permissions" ON "members_permissions"."permission_id" = "permissions"."id"
LEFT OUTER JOIN "members" ON "members"."id" = "members_permissions"."member_id" 
  AND "permissions"."name" = 'organiser'

Why tests don't fail: The test factories create workshops without individual organiser permissions (only chapter-level), so N+1 doesn't trigger in tests. The N+1 would appear in production when workshops/events have specific organiser permissions.

Testing in production:

1. Enable query logging in development
2. Visit the homepage
3. Look for "Permission Load" queries - with the fix, they should NOT appear inside the event iteration loop

[KimberleyCook]

🎉