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/app/services/admin/host_metrics.rb

@@ -84,26 +84,57 @@ module Admin
     def disk_usage_for(path)
       return unavailable_disk unless path.present? && (Dir.exist?(path) || File.exist?(path))
 
+      usage = disk_usage_via_statvfs(path) || disk_usage_via_df(path)
+      return unavailable_disk unless usage
+
+      usage.merge(dir_size_bytes: recordings_dir_size(path))
+    rescue StandardError
+      unavailable_disk
+    end
+
+    def disk_usage_via_statvfs(path)
+      return nil unless File.respond_to?(:statvfs)
+
       stat = File.statvfs(path)
       total = stat.blocks * stat.frsize
       free = stat.bavail * stat.frsize
       used = total - free
+      build_disk_usage(path, total: total, used: used, free: free)
+    rescue StandardError
+      nil
+    end
+
+    def disk_usage_via_df(path)
+      output = shell_out("df -B1 --output=size,used,avail,pcent,target #{Shellwords.escape(path)} 2>/dev/null").strip
+      line = output.lines.map(&:strip).reject(&:blank?).last
+      return nil if line.blank? || line.start_with?("Filesystem")
+
+      parts = line.split
+      return nil if parts.size < 5
+
+      total = parts[0].to_i
+      used = parts[1].to_i
+      free = parts[2].to_i
+      pct = parts[3].delete("%").to_f
+      build_disk_usage(path, total: total, used: used, free: free, used_percent: pct)
+    rescue StandardError
+      nil
+    end
+
+    def build_disk_usage(path, total:, used:, free:, used_percent: nil)
       {
         path: path,
         total_bytes: total,
         used_bytes: used,
         free_bytes: free,
-        used_percent: total.positive? ? ((used.to_f / total) * 100).round(1) : 0.0,
-        dir_size_bytes: recordings_dir_size(path)
+        used_percent: used_percent || (total.positive? ? ((used.to_f / total) * 100).round(1) : 0.0)
       }
-    rescue StandardError
-      unavailable_disk
     end
 
     def recordings_dir_size(path)
       return nil unless path == RECORDINGS_PATH && Dir.exist?(path)
 
-      `du -sb #{Shellwords.escape(path)} 2>/dev/null`.split.first.to_i
+      shell_out("du -sb #{Shellwords.escape(path)} 2>/dev/null").split.first.to_i
     rescue StandardError
       nil
     end
@@ -112,6 +143,10 @@ module Admin
       { path: nil, total_bytes: nil, used_bytes: nil, free_bytes: nil, used_percent: nil, dir_size_bytes: nil }
     end
 
+    def shell_out(cmd)
+      `#{cmd}`
+    end
+
     def read_network
       rx, tx = parse_net_bytes
       prev = MetricsStore.net_totals