Override personal channel close settings in shared inboxes

Problem
When a personal channel conversation is merged into a shared inbox, the personal channel's close settings take priority over the shared inbox's settings — even though the conversation is now in the team inbox. Admins have no way to audit individual personal channel close settings without checking each teammate's configuration manually.

Request
Give shared inbox close settings precedence over personal channel close settings when conversations are merged into a shared inbox, and provide an admin view to audit personal channel close settings across all teammates.