Keep navigation-bar's own example in step with the scaffold's rewrite

Its header comment quoted <x-scaffold>'s old Tailwind wrapper class
list verbatim; the scaffold now draws that wrapper on data-md-scaffold-bar,
so the example follows.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/views/components/navigation-bar.blade.php

@@ -1,7 +1,7 @@
 {{-- M3 Expressive's flexible navigation bar: three to five destinations at the bottom of a
      compact window.
 
-         <div class="fixed inset-x-0 bottom-0 z-30 medium:hidden">
+         <div data-md-scaffold-bar>
              <x-navigation-bar>
                  <x-navigation-bar-item label="Inbox" icon="inbox" link="/inbox" active badge="12" />
                  <x-navigation-bar-item label="Starred" icon="star" link="/starred" />