Automatic pruning with staff confirmation (CBOT-16)

[waregin]

From JIRA CBOT-16 (Backlog, 2022). Rules from the ticket:

• no bans, only kicks for pruning
• never prune anyone level 5 or above
• never prune anyone who joined since the last prune
• never prune anyone who has been active since the last prune
• report: "here's everyone level 5+ who hasn't been active for over a year"
• confirmation flow: "here's all the users I think I should prune, please confirm" with an exclude command that republishes the list minus excluded names

Human confirmation before any kick is a hard requirement.