Existing API Client transition strategy following digital acceptance implementation

**Background**:

Today the process for signing API agreement is:

API Vendor downloads the ToU.
API Vendor signs the ToU.
Business Registry staff review and file the signed agreement on the LAN.
API key is issued.
Signed agreement is retained as evidence of acceptance.

With digital acceptance, we need a strategy for existing clients who have already signed under the old process.

Define how existing API clients who previously completed the manual ToU process will be managed following implementation of digital ToU acceptance, including handling of historical agreements, client communications, acceptance requirements, and record retention.

The issue body is the only stated entry point; no files, tests, or implementation entry points are mentioned. Start by reviewing the current manual and digital ToU acceptance processes, then document a transition strategy covering historical agreements, client communications, acceptance requirements, and record retention.

Written by the indexing model from the issue text.