Frosted bottom bar: adjustable blur and opacity with Less/Default/More presets

Settings > Appearance shows a preset control plus Blur and Opacity sliders
(new NooSlider) while frosted glass is on; values persist and feed
NooBottomBar.frostedBlur/frostedOpacity. Default matches the old fixed look.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

lib/main.dart

@@ -564,6 +564,8 @@ class _MainShellViewState extends State<MainShellView> {
           style: navStyle,
           barStyle: bottomBarStyle,
           frosted: settings.bottomBarFrosted,
+          frostedBlur: settings.bottomBarFrostedBlur,
+          frostedOpacity: settings.bottomBarFrostedOpacity,
           tabs: pinnedTabs,
           selectedIndex: pinnedIndex,
           onSearchTap: showBottomBarSearch ? () => openSearch(context) : null,