Add avatar-menu navigation style and inline Android search bar

- New Settings > Appearance > "Navigation menu" toggle
  (SettingsController.navMenuStyle, NooNavMenuStyle.drawer/avatarMenu):
  the hamburger-opens-a-Drawer pattern stays the default, or the avatar
  button opens a full-width dropdown (showAvatarMenu) instead, holding
  the same hidden-tabs + Settings content the drawer does. Removes one
  of the two top-corner targets the shell asks a thumb to reach, with
  no permanent chrome added.
- NooTopBar gains androidTitleReplacement so Android's top bar can swap
  its title for an inline search-field-styled launcher
  (ShellSearchLauncher) when search isn't in the bottom bar, instead of
  a bare search icon beside it.
- ShellAvatarButton's onTap/label are now overridable so AppTopBar can
  repoint it per the new setting without this file depending on
  avatar_menu.dart (which already depends on it for shared helpers).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/main.dart

@@ -423,6 +423,7 @@ class _MainShellViewState extends State<MainShellView> {
                           style: navStyle,
                           tab: tab,
                           searchInBottomBar: showBottomBarSearch,
+                          navMenuStyle: settings.navMenuStyle,
                         ),
                 ),
               )