Warn before a teammate group edit removes inbox access

Problem
When editing or deleting a teammate group, there is no warning that the change will remove inbox or workspace access for teammates who only had that access through the group. The access disappears the moment the change is saved.

Request
Before saving an edit that removes access, show a warning listing the teammates who will lose inbox or workspace access as a result, and ask for confirmation.

Context
An admin reorganizing teammate groups can lock an entire team out of their inboxes without realizing it, because access granted only through the edited group is revoked immediately and silently.