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.

tasks/ch21-30.md

@@ -360,21 +360,30 @@
 - [x] StickerPicker
 - [x] GifPicker — host images
 
-## T29 Mail — `src/mail`
+## T29a Mail · Boxes and lists — `src/mail`
+
+- [x] MailboxList / FolderList
+- [x] MailList
+- [x] MailItem
+- [x] InboxZeroState → `feedback::EmptyState`
+
+## T29b Mail · Reading
 
-- [ ] MailboxList / FolderList
-- [ ] MailList
-- [ ] MailItem
 - [ ] MailReader
-- [ ] MailComposer
-- [ ] RecipientInput
 - [ ] MailThreadView
 - [ ] QuotedText
+
+## T29c Mail · Writing
+
+- [ ] MailComposer
+- [ ] RecipientInput
 - [ ] SignatureEditor
+- [ ] ScheduleSend
+
+## T29d Mail · Sorting
+
 - [ ] LabelPicker
 - [ ] SnoozePicker
-- [ ] ScheduleSend
-- [ ] InboxZeroState
 
 ## T30 Calendar — `src/calendar`