Completa il hardening autoscaler (Fase 4): budget, kill-switch e runbook.

Drain sicuro in scale-in, alert Ops su overflow e controlli admin senza abilitare il deploy in produzione.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/config/routes.rb

@@ -114,6 +114,10 @@ Rails.application.routes.draw do
       member do
         post :drain
       end
+      collection do
+        post :kill_switch
+        delete :clear_kill_switch
+      end
     end
     get "youtube/platform", to: "youtube#platform", as: :youtube_platform
   end