Put address books in the left pane, other people's included

Address book sharing was withdrawn a few hours ago on a report that it
behaved like mail folder sharing. That was wrong -- it works -- and it is
back, built the way Files is rather than the way it was.

Three things it inherits from Files. Shared books are listed in the app's
own left pane instead of behind an account switch in the profile menu.
The reader's books and other people's sit under separate headings, since
a book belonging to somebody else behaves differently and a single merged
list would be quiet about whose contacts you are reading. And opening
Contacts re-reads the session, so a book shared while the tab was open
turns up without signing out and in again.

The books pane the view kept to itself is gone, and with it the last
module that ignored the sidebar it was given.

The one thing Files does not need: shared contacts have to answer when
somebody types a name into a To field, so they are loaded up front rather
than when a book is opened, and they are offered by `suggest` and found
by `lookupByEmail` alongside the reader's own. Their own cards win a tie,
since a card someone wrote themselves should beat a colleague's copy of
the same person. That is the difference between a shared book you can
look at and one you can use.

Cards from a shared account are held apart from the reader's rather than
merged in, and keyed by account as well as id. Ids are only unique within
an account -- two accounts each having a book `ab1` is ordinary -- and a
flat map would have had one silently replace the other.

The mock grew an address book in its shared account, with contacts in it,
because none of this could be exercised otherwise.

KNOWN-ISSUES records the withdrawal as the mistake it was rather than
leaving it in the history looking like a finding. Mail folder sharing
stays withdrawn: that one really is broken.

web/src/views/AppShell.tsx

@@ -10,6 +10,7 @@ import { MenuItem, MenuSep, MenuTitle, Popover, useMenu } from "@/ui/popover";
 import { SearchBar } from "./SearchBar";
 import { MailboxTree } from "./mail/MailboxTree";
 import { FilesTree } from "./files/FilesTree";
+import { ContactsSidebar } from "./contacts/ContactsSidebar";
 import { CalendarSidebar } from "./calendar/CalendarSidebar";
 import { ShortcutsDialog, useGlobalShortcuts } from "./Shortcuts";
 import { formatSize } from "@/lib/format";
@@ -131,7 +132,7 @@ export function AppShell({ children }: { children: ReactNode }) {
           <div className="sidebar-scroll">
             {(section === "mail" || section === "search") && <MailboxTree />}
             {section === "calendar" && <CalendarSidebar />}
-            {section === "contacts" && <div className="nav-section"><span>Contacts</span></div>}
+            {section === "contacts" && <ContactsSidebar />}
             {section === "files" && <FilesTree />}
             {section === "settings" && <div className="nav-section"><span>Settings</span></div>}
           </div>