Load the composer, previews, dialogs and other sidebars on demand

The main chunk carried everything the mail view might open: the file
preview and its Markdown renderer, the composer and its editor, the contact
editor, the filter and share dialogs, and the calendar, contacts and files
sidebars. Each is now loaded when first shown. The composer is also
fetched when the browser is idle after startup, so the first Compose does
not wait on the network.

Import the notification helpers statically where they already were: the
dynamic imports beside those static ones split nothing.

web/src/views/mail/AddressMenu.tsx

@@ -1,4 +1,4 @@
-import { useCallback, useState, type MouseEvent, type ReactNode } from "react";
+import { lazy, Suspense, useCallback, useState, type MouseEvent, type ReactNode } from "react";
 import { Copy, Mail, Pencil, UserPlus } from "lucide-react";
 import type { EmailAddress } from "@/jmap/types";
 import { useContacts } from "@/store/contacts";
@@ -7,9 +7,11 @@ import { contactFromAddress } from "@/lib/contacts";
 import { formatAddress } from "@/lib/address";
 import { MenuItem, MenuSep, Popover, type Anchor } from "@/ui/popover";
 import { toast } from "@/ui/toast";
-import { ContactEditor } from "../contacts/ContactEditor";
 import { t } from "@/lib/i18n";
 
+// Loaded when first opened: it is not needed to show mail, and it is not small.
+const ContactEditor = lazy(() => import("../contacts/ContactEditor").then((m) => ({ default: m.ContactEditor })));
+
 /**
  * Right-click on anyone named in a message — sender, recipients, Reply-To — to
  * add them to the address book. The contact editor opens prefilled rather than
@@ -65,12 +67,14 @@ export function useAddressMenu() {
         </Popover>
       )}
       {editing && (
+        <Suspense fallback={null}>
         <ContactEditor
           card={editing}
           defaultBookId={defaultBookId}
           onClose={() => setEditing(null)}
           onSaved={() => setEditing(null)}
         />
+        </Suspense>
       )}
     </>
   );