Designated primary form owner for shared forms

## Description

Clarity on who owns the form and how ownership transfers

## Context

As we've added collaboration features, it's becoming more important to know who is the form or service owner and who should be contacted in case of a problem.

https://cds-snc.freshdesk.com/a/tickets/28813
> A wishlist of items for shared forms: Designate a “primary” editor/owner for the form Let primary undo recent changes done by others

From another support ticket:

> "If I share a GC Form with a colleague using the "Manage access" feature, does that make them a co-owner of the form? Specifically if my Government of Canada account is deleted in the future, will the form continue to exist because it has been shared with my colleague, or will it be deleted?"

No files or tests are named. Start by tracing the shared-form Manage access flow in the platform-forms-client application and review the linked support requests for ownership and account-deletion requirements. Done means the primary owner is defined, ownership transfer is addressed, and the form's behavior when that account is deleted is clear and verified.

Written by the indexing model from the issue text.