Add a floating bottom bar style, user-configurable in Settings

Settings > Appearance > "Bottom bar" now switches between the
original edge-to-edge bar and a floating one - inset 16px from both
side edges and clear of the bottom safe area, 28px corners (the same
radius the sheet top/drawer edge use), a 1px line border standing in
for elevation instead of a shadow (product UI stays flat). Persisted
via NooBottomBarStyle, defaulting to the existing attached behavior.

On Android, floating's idle tabs drop their reserved label space -
with no label to leave room for, the icon centers in the whole button
and renders a touch bigger (27 vs 24px) instead of sitting high with a
gap held open under it; the active tab's icon/pill/label position is
unchanged. iOS's tab content is unchanged either way, only the
container.

main.dart sets Scaffold.extendBody while floating so the body scrolls
behind the bar's transparent margin instead of stopping short of it,
matching how the design canvas explored it.

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

lib/main.dart

@@ -472,6 +472,7 @@ class _MainShellViewState extends State<MainShellView> {
       );
     } else {
       final navStyle = NooLayout.navStyle(context);
+      final bottomBarStyle = settings.bottomBarStyle;
       scaffold = Scaffold(
         backgroundColor: colors.bg,
         drawerScrimColor: colors.scrim,
@@ -479,6 +480,10 @@ class _MainShellViewState extends State<MainShellView> {
             ? AppTopBar(style: navStyle, tab: selectedTab)
             : null,
         drawer: pickRequest == null ? const AppDrawer() : null,
+        // Floating needs the body to draw behind the bar's own transparent
+        // margin (see NooBottomBarStyle's doc comment) instead of stopping
+        // short of it like attached does.
+        extendBody: bottomBarStyle == NooBottomBarStyle.floating,
         // Android-only extended Upload FAB - iOS uses the top bar's `plus`
         // instead (see AppTopBar). Stays mounted across every tab (picking
         // aside) and collapses to an icon-only circle off Files/Photos,
@@ -494,6 +499,7 @@ class _MainShellViewState extends State<MainShellView> {
         body: tabStack,
         bottomNavigationBar: BottomNavBar(
           style: navStyle,
+          barStyle: bottomBarStyle,
           tabs: pinnedTabs,
           selectedIndex: pinnedIndex,
           onDestinationSelected: (index) {