Bottom bar: add frosted glass option (Settings > Appearance)

Translucent fill over a backdrop blur, both platforms and both bar styles.
Frosted bars draw over an extended body, so the shell's extendBody and the
tab clearance now key off NooBottomBar.drawsBehindBody.

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

lib/views/files_view.dart

@@ -837,10 +837,13 @@ class _FilesViewState extends State<FilesView> {
         ),
       // List/grid/table above only pad NooSpace.lg at the bottom - plenty
       // once Scaffold shrinks the body above an attached bar, but floating
-      // draws the body behind the bar instead, so it needs the bar's own
-      // footprint added on top or the last row ends up under it.
-      if (context.watch<SettingsController>().bottomBarStyle ==
-          NooBottomBarStyle.floating)
+      // draws the body behind the bar instead (as does a frosted bar), so it
+      // needs the bar's own footprint added on top or the last row ends up
+      // under it.
+      if (NooBottomBar.drawsBehindBody(
+        context.watch<SettingsController>().bottomBarStyle,
+        context.watch<SettingsController>().bottomBarFrosted,
+      ))
         SliverToBoxAdapter(
           child: SizedBox(height: bottomBarClearance(context)),
         ),