Events: kickstart shared scoreboard

app/views/events/show.html.slim

@@ -8,7 +8,14 @@
         a.mt-3.btn.btn-primary.mb-4 href=new_contest_path(event: @event.id)
           = t("events.show.new_contest")
 
-.row.row-cols-1.row-cols-md-3.g-4
+- if @event.shared_scoreboard
+  a.btn.btn-success href="/public/event/#{@event.slug}" style="margin-top: -6px;"
+    = t("events.show.open_shared_scoreboard")
+- else
+  a.btn.btn-success.disabled style="margin-top: -6px;"
+    = t("events.show.shared_scoreboard_disabled")
+
+.mt-3.row.row-cols-1.row-cols-md-3.g-4
   - @contests.each do |contest|
     .col
       css: