Aggiunge monitoraggio ops: health check, log scanner, dashboard e notifiche.

Introduce incidenti con dedup, job Sidekiq ogni 3 min, scan log cron, /up/deep,
dashboard /admin/ops e push ntfy; include Sentry opzionale e fix test suite.

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

backend/spec/services/youtube/broadcast_service_spec.rb

@@ -4,10 +4,10 @@ RSpec.describe Youtube::BroadcastService do
   describe "#normalize_scheduled_start_time" do
     subject(:service) { described_class.allocate }
 
-    it "usa tra ~90 secondi se scheduled_at è assente" do
+    it "usa tra ~20 secondi se scheduled_at è assente" do
       travel_to Time.zone.parse("2026-06-03 20:00:00 UTC") do
         t = service.send(:normalize_scheduled_start_time, nil)
-        expect(t).to eq(Time.utc(2026, 6, 3, 20, 1, 30))
+        expect(t).to eq(Time.utc(2026, 6, 3, 20, 0, 20))
       end
     end
 
@@ -15,7 +15,7 @@ RSpec.describe Youtube::BroadcastService do
       travel_to Time.zone.parse("2026-06-03 20:00:00 UTC") do
         past = Time.zone.parse("2026-06-03 10:00:00")
         t = service.send(:normalize_scheduled_start_time, past)
-        expect(t).to eq(Time.utc(2026, 6, 3, 20, 1, 30))
+        expect(t).to eq(Time.utc(2026, 6, 3, 20, 0, 20))
       end
     end