Introduces the ability for users with the **Assistant** role to prefill
fields on behalf of other signers. Assistants can fill in various field
types such as text, checkboxes, dates, and more, streamlining the
document preparation process before it reaches the final signers.
Implements a bulk send feature allowing users to upload a CSV file to
create multiple documents from a template. Includes CSV template
generation, background processing, and email notifications.
