Add "Search in bottom bar" to Settings

New Settings > Appearance toggle moves Search into the bottom bar and
out of the top bar, so there's only one search entry point on screen.
Tapping it pushes SearchView same as before - it's never highlighted,
since it isn't a real destination.

- Attached: Search becomes the row's last item, styled like any other
  tab but permanently idle.
- Floating: Search gets its own separate, always fully round satellite
  circle beside the bar instead.

Enabling it costs one regular tab: SettingsController.maxVisibleTabs
is now a dynamic getter (defaultMaxVisibleTabs - 1 while the toggle is
on) instead of the old flat constant, re-enforced immediately if the
user already has all 5 slots filled - the same cleanup path used for
a fresh install or an app update that added a new tab.

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

lib/widgets/app_top_bar.dart

@@ -19,13 +19,24 @@ import 'shell/shell_common.dart';
 /// [style] is resolved by the caller (`NooLayout.navStyle`) rather than
 /// read from context here, since [preferredSize] is a plain getter with no
 /// BuildContext - the same reason [NooTopBar] itself takes it as a field.
+/// [searchInBottomBar] is [SettingsController.searchInBottomBar], passed in
+/// for the same reason: it hides this bar's own search field/icon so
+/// there's only ever one search entry point on screen once the bottom bar
+/// has taken it over.
 class AppTopBar extends StatelessWidget implements PreferredSizeWidget {
   final NooNavStyle style;
   final AppTab tab;
+  final bool searchInBottomBar;
 
-  const AppTopBar({super.key, required this.style, required this.tab});
+  const AppTopBar({
+    super.key,
+    required this.style,
+    required this.tab,
+    this.searchInBottomBar = false,
+  });
 
   bool get _ios => style == NooNavStyle.ios;
+  bool get _showSearch => !searchInBottomBar;
 
   @override
   Size get preferredSize => NooTopBar(
@@ -34,7 +45,7 @@ class AppTopBar extends StatelessWidget implements PreferredSizeWidget {
     // A throwaway placeholder purely to make preferredSize's "is there a
     // search slot" check match what build() actually shows - never
     // inserted into the tree, so its content doesn't matter.
-    search: _ios ? const SizedBox.shrink() : null,
+    search: _ios && _showSearch ? const SizedBox.shrink() : null,
   ).preferredSize;
 
   @override
@@ -44,7 +55,7 @@ class AppTopBar extends StatelessWidget implements PreferredSizeWidget {
       title: tab.label,
       onMenu: () => Scaffold.of(context).openDrawer(),
       actions: [
-        if (!_ios)
+        if (!_ios && _showSearch)
           NooTopBarButton(
             icon: LucideIcons.search,
             tooltip: 'Search',
@@ -58,7 +69,7 @@ class AppTopBar extends StatelessWidget implements PreferredSizeWidget {
           ),
         ShellAvatarButton(hitBox: _ios ? 44 : 48),
       ],
-      search: _ios ? const ShellSearchLauncher(ios: true) : null,
+      search: _ios && _showSearch ? const ShellSearchLauncher(ios: true) : null,
     );
   }
 }