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/widgets/noo/nav/noo_nav_style.dart

@@ -32,6 +32,20 @@ enum NooNavStyle {
 /// trailing padding to clear the bar (see `NooBottomBar.rowHeight`).
 enum NooBottomBarStyle { attached, floating }
 
+/// Which widget opens the shell's navigation menu (hidden tabs + Settings)
+/// on mobile - user-configurable in Settings (Appearance), same precedent
+/// as [NooBottomBarStyle]. [drawer] is the original pattern: a `menu`
+/// icon, top-left of the top bar, opens a left-edge `Drawer`. [avatarMenu]
+/// drops that icon entirely and repurposes the avatar button - already
+/// sitting top-right, already a tap target every user already knows - as
+/// the one entry point instead, opening a dropdown anchored below it (see
+/// `showAvatarMenu` in `widgets/avatar_menu.dart`) rather than a drawer
+/// sliding from the opposite edge. Applies on both platforms, since
+/// [NooTopBar]'s `onMenu`/avatar wiring is shared chrome, not
+/// Android-specific - only [AppDrawer]'s left-`Drawer` convention is being
+/// offered an alternative, not anything platform-only.
+enum NooNavMenuStyle { drawer, avatarMenu }
+
 /// One destination in a [NooBottomBar]. Data-agnostic on purpose - the app
 /// maps its own tab model (e.g. `AppTab`) onto these.
 @immutable

lib/widgets/noo/nav/noo_top_bar.dart

@@ -56,6 +56,15 @@ class NooTopBar extends StatelessWidget implements PreferredSizeWidget {
   /// iOS only: the search field shown below the large title.
   final Widget? search;
 
+  /// Android only: replaces the plain title text with an arbitrary widget
+  /// (e.g. a search-field-styled launcher) in that same flexible middle
+  /// slot, between [leading]/the menu button and [actions]. iOS already
+  /// has a dedicated [search] slot below its large title for this; Android
+  /// has no large title to put a second row under, so a caller that wants
+  /// an inline search bar there replaces the title with one instead of
+  /// adding a row.
+  final Widget? androidTitleReplacement;
+
   /// Defaults to `bg` - the top bar sits on the screen background.
   final Color? backgroundColor;
 
@@ -67,6 +76,7 @@ class NooTopBar extends StatelessWidget implements PreferredSizeWidget {
     this.onMenu,
     this.actions = const [],
     this.search,
+    this.androidTitleReplacement,
     this.backgroundColor,
   });
 
@@ -179,12 +189,14 @@ class NooTopBar extends StatelessWidget implements PreferredSizeWidget {
           children: [
             ?lead,
             Expanded(
-              child: Text(
-                title,
-                maxLines: 1,
-                overflow: TextOverflow.ellipsis,
-                style: NooText.title.copyWith(height: 1, color: colors.fg1),
-              ),
+              child:
+                  androidTitleReplacement ??
+                  Text(
+                    title,
+                    maxLines: 1,
+                    overflow: TextOverflow.ellipsis,
+                    style: NooText.title.copyWith(height: 1, color: colors.fg1),
+                  ),
             ),
             ...actions,
           ],