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/settings/settings_tabs.dart

@@ -11,7 +11,8 @@ import '../noo/noo_layout.dart';
 import 'settings_section.dart';
 
 /// Settings section 7: bottom-nav tab order, visibility (pinned = shown, up
-/// to [maxVisibleTabs]) and default tab.
+/// to [SettingsController.maxVisibleTabs] - one fewer while Appearance's
+/// "Search in bottom bar" is on) and default tab.
 class SettingsTabsSection extends StatelessWidget {
   const SettingsTabsSection({super.key});