Require visitors to accept an NDA before accessing restricted Trust Center documents

As a Trust Center admin, I want to require visitors to accept or sign an NDA before they can request or open restricted documents, so I don't have to handle NDAs manually by email.

What would help:
- Upload our own NDA template (or use a standard one) and choose which documents require it
- Visitors accept/sign the NDA as part of the access request flow
- The signed NDA is stored with the access request so we can show it to auditors
- NDA acceptance can be used as a condition for auto-approving access.