Integrate InvitationLogger for event invitation sending

[mroderick]

Events are the only invitation type without InvitationLogger logging. Workshops and virtual workshops record batch progress to InvitationLog per member (success/failure/skipped, total count, batch status). Events don't. When a batch fails, tracking who received what requires manual correlation across DJ logs and email delivery logs.

Add the same logging pattern to InvitationManager#send_event_emails that already exists for workshops:

app/services/invitation_manager.rb

• Add initiator_id param to send_event_emails
• Look up Member from initiator_id; create InvitationLogger.new(event, initiator, audience, :invite)
• Call logger.start_batch, finish_batch(total), fail_batch(e) — catch ActiveRecord::RecordNotUnique on start_batch to prevent duplicate batches
• Thread logger through invite_students_to_event and invite_coaches_to_event so each member outcome is logged

Open question: events send to both Students and Coaches in one call. InvitationLogger expects a single audience. Use a combined audience value (e.g. everyone) or log two separate batches.

app/controllers/admin/events_controller.rb

• Pass current_user.id to send_event_emails

Tests

• Add to spec/services/invitation_manager_spec.rb or spec/services/invitation_manager_logging_spec.rb

Migration

None. InvitationLog#loggable is polymorphic and already accepts Event. InvitationLog#action enum supports invite. audience is a string column.

Context

• Workshop reference: InvitationManager#send_workshop_emails (line ~46), invite_members, send_email_with_logging
• InvitationLog fields: loggable (polymorphic), initiator (Member), chapter_id, audience, action, status, total_invitees, timestamps

Out of scope

• send_meeting_emails — separate concern