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/locales/admin.en.yml

@@ -30,6 +30,8 @@ en:
       stream_node_created: "Lab node %{slug} provisioned."
       stream_node_destroyed: "Node %{slug} removed."
       stream_node_draining: "Node %{slug} is draining (no new sessions)."
+      autoscale_kill_on: "Autoscaler kill-switch engaged. No automatic scale-out."
+      autoscale_kill_off: "Autoscaler kill-switch cleared (still needs STREAM_AUTOSCALE_ENABLED=1)."
       comped_granted: "%{plan} complimentary subscription activated for %{club}."
       comped_revoked: "Complimentary subscription revoked for %{club}."
       session_already_terminated: "Session already ended (%{status})."
@@ -119,6 +121,11 @@ en:
       title: Streaming nodes
       providers: "Cloud provider: %{cloud} · DNS provider: %{dns}"
       autoscale: "Autoscaler %{enabled} · free_slots=%{free} (soft≤%{soft}) · spare=%{spare}/%{warm} · overflow=%{overflow}/%{max} · kind=%{kind}"
+      autoscale_budget: "budget €%{eur}/€%{budget} (%{ok})"
+      kill_switch_active: "KILL-SWITCH ACTIVE"
+      engage_kill_switch: "Kill-switch ON (block autoscaler)"
+      clear_kill_switch: "Kill-switch OFF"
+      kill_switch_confirm: "Immediately block the autoscaler? Existing nodes stay up."
       provision_lab: Provision lab node
       provision_cloud: Provision Hetzner node
       provision_cloud_confirm: "Create a Hetzner Cloud server + DNS record on mltv-stream.net? Billing applies until destroyed."