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/Gemfile.lock

@@ -381,6 +381,13 @@ GEM
       rubocop-rails (>= 2.30)
     ruby-progressbar (1.13.0)
     securerandom (0.4.1)
+    sentry-rails (6.6.2)
+      railties (>= 5.2.0)
+      sentry-ruby (~> 6.6.2)
+    sentry-ruby (6.6.2)
+      bigdecimal
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      logger
     sidekiq (8.1.5)
       connection_pool (>= 3.0.0)
       json (>= 2.16.0)
@@ -456,6 +463,8 @@ DEPENDENCIES
   redis (>= 4.0.1)
   rspec-rails
   rubocop-rails-omakase
+  sentry-rails
+  sentry-ruby
   sidekiq
   stripe
   tzinfo-data