ChannelList sets chats down in sections, each a list: a press, an arrow
or Enter opens one, and the open chat is lit. A title names one section,
and a section holds a chat. ChannelItem shows a hash or a lock, its
unread count, a pin when pinned, and goes quiet when muted.
DirectMessageItem shows a person's initials with their presence. Unread
names stand out through ListItem's new strong; muted channels and
offline people go quiet through its quiet. ChannelHeader holds the name
and topic beside members, pins and a call, wrapping by the header rule.
PinnedMessages lists pins newest first; a press, an arrow or Enter opens
one, and Unpin lets one go. With none it shows a line and takes no Tab
stop.