DoppelBrand: Forged forwarded email thread simulating prior ServiceNow exec conversation

Detects inbound emails that spoof ServiceNow branding or impersonate high-level organizational roles (e.g., CEO, VP, President) in the display name while using common reply/forward subject headers. The rule specifically flags these if the sender domain does not originate from a legitimate service-now.com domain and contains PDF or HTML attachments, which are common vectors for credential harvesting or malware delivery.