Mail · Boxes and lists: mailboxes, folders and labels, the mail list, inbox zero

MailboxList sets mailboxes, folders and labels in sections: a press, an
arrow or Enter opens one, the open one lit; a box with mail unread
stands out with its count, and a label wears one of the theme's chart
hues. MailList holds messages in a multiple-select list: the sender
strong beside a dot while unread, the subject and first words under
it, the time today, the weekday this week, the date this year or with
its year, a paperclip for files, and a star whose press stays off the
row. InboxZeroState points to feedback::EmptyState.

Sections of selectable lists now have one home, lists::Sections, which
ChannelList and MemberList use too; ListItem gains a third line.

assets/icons/octagon-alert.svg

@@ -0,0 +1,17 @@
+<!-- @license lucide-static v1.48.0 - ISC -->
+<svg
+  class="lucide lucide-octagon-alert"
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <path d="M12 16h.01" />
+  <path d="M12 8v4" />
+  <path d="M15.312 2a2 2 0 0 1 1.414.586l4.688 4.688A2 2 0 0 1 22 8.688v6.624a2 2 0 0 1-.586 1.414l-4.688 4.688a2 2 0 0 1-1.414.586H8.688a2 2 0 0 1-1.414-.586l-4.688-4.688A2 2 0 0 1 2 15.312V8.688a2 2 0 0 1 .586-1.414l4.688-4.688A2 2 0 0 1 8.688 2z" />
+</svg>