Better visual marking of recent ticket activity

[p10e]

Slack does a pretty good job of showing activity in threads and notifying agents to take action. However, sometimes replies slip through the cracks when using Slack's Threads view and everything is instantly marked as read. Additionally, Slack does not offer any neat list view of active threads. For agents, it would be convenient to also keep track of recent activity in the Studio's ticket list.

As we cannot track what agents see on Slack, having read/unread statuses in the Studio does not make sense in this case. Instead, we could add an activity dot to topics that have non-agent responses within the last 24 hours, for example. On the other end of the spectrum, we might also want to highlight open tickets that have not received an agent update/reply for the past 48 hours, for example. Or we could mark both of these differently, e.g. blue dots for recent activity and red dots for expiring tickets.