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/app/views/admin/stream_nodes/index.html.erb

@@ -16,6 +16,15 @@
         max: @autoscale_metrics[:max_overflow_nodes],
         kind: @autoscale_metrics[:kind]
       ) %>
+  · <%= t(
+        "admin.stream_nodes.autoscale_budget",
+        eur: @autoscale_metrics[:estimated_monthly_eur],
+        budget: @autoscale_metrics[:monthly_budget_eur],
+        ok: (@autoscale_metrics[:within_budget] ? "OK" : "OVER")
+      ) %>
+  <% if @autoscale_metrics[:kill_switch] %>
+    · <strong><%= t("admin.stream_nodes.kill_switch_active") %></strong>
+  <% end %>
 </p>
 
 <p>
@@ -26,6 +35,12 @@
   <% else %>
     <span class="admin-muted"><%= t("admin.stream_nodes.hetzner_token_missing") %></span>
   <% end %>
+  <% if @autoscale_metrics[:kill_switch] %>
+    <%= button_to t("admin.stream_nodes.clear_kill_switch"), clear_kill_switch_admin_stream_nodes_path, method: :delete, class: "admin-btn admin-btn-secondary" %>
+  <% else %>
+    <%= button_to t("admin.stream_nodes.engage_kill_switch"), kill_switch_admin_stream_nodes_path, method: :post, class: "admin-btn admin-btn-danger",
+          form: { data: { confirm: t("admin.stream_nodes.kill_switch_confirm") } } %>
+  <% end %>
 </p>
 
 <table class="admin-table">