Remove rerolled user from theme roster and notify channel

Your theme chooser entries get stuck after rerolls, leaving the roster inaccurate and causing duplicate selections. It fixes the roster and notifies the channel so coordinators get accurate choices same day.

Overview

Rerolls often leave your chooser list out of sync and force manual cleanups, slowing weekly ops. This flow fixes the roster and posts a channel update immediately so coordinators and IT have accurate choices the same day.