ConferencesController#index: redirect to latest sponsorship when no open conferences

Previously showed a blank page when logged in but no conference
had applications open. Now falls back to the user's most recent
active sponsorship.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sorah

app/controllers/conferences_controller.rb

@@ -6,6 +6,8 @@ def index
 
     if @conferences.one?
       redirect_to user_conference_sponsorship_path(@conferences.first)
+    elsif @conferences.empty? && current_available_sponsorships&.exists?
+      redirect_to user_conference_sponsorship_path(current_available_sponsorships.first.conference)
     end
   end
 end