The button and slash close paths deleted the channel via a bare setTimeout that
never set the pendingDelete flag, so a restart in the 5s grace window orphaned
the channel (closed in DB, still present in Discord) with no recovery — only the
auto-close path used the flag correctly.
Extract scheduleTicketChannelDelete() in services/tickets.js: a grace-delayed,
queue-routed (enqueueDelete) delete that clears pendingDelete on success. All
three close paths now use it. Button/slash set pendingDelete:true and keep
discordThreadId populated so resumePendingDeletes() recovers the delete on the
next boot. The button path previously nulled discordThreadId before the delete,
which made the channel unrecoverable.
