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/db/migrate/20260611120000_create_ops_incidents.rb

@@ -0,0 +1,26 @@
+class CreateOpsIncidents < ActiveRecord::Migration[7.2]
+  def change
+    create_table :ops_incidents, id: :uuid do |t|
+      t.string :kind, null: false
+      t.string :severity, null: false, default: "warning"
+      t.string :status, null: false, default: "open"
+      t.string :title, null: false
+      t.text :message
+      t.jsonb :metadata, null: false, default: {}
+      t.string :fingerprint, null: false
+      t.integer :occurrence_count, null: false, default: 1
+      t.datetime :first_seen_at, null: false
+      t.datetime :last_seen_at, null: false
+      t.datetime :notified_at
+      t.datetime :acknowledged_at
+      t.datetime :muted_until
+
+      t.timestamps
+    end
+
+    add_index :ops_incidents, :fingerprint
+    add_index :ops_incidents, %i[status severity]
+    add_index :ops_incidents, :last_seen_at
+    add_index :ops_incidents, %i[fingerprint status]
+  end
+end