This fix prevents automated email scanners from accidentally changing the status of signature requests. Previously, security scanners that check links in emails could trigger HTTP HEAD requests that would mark sign requests as ignored without any user action. Now the system properly handles these scanner requests so they don't affect the actual signature workflow.

Issue:
Mail scanners can send HTTP HEAD requests to links contained in emails, which can change the state of a sign request without user action.

Steps:
- send a sign request
- look in mailhog to get the notification mail
- copy the link at the bottom of the mail and `curl --head <url>`
- the sign request is now ignored

opw-4217355