Stop drawing each section's title twice on its page

Plan step 38 review: the frame's structural rule that kept a section's
own <h2> for screen readers (Tailwind's [&>section>h2]:sr-only before,
a showcase.css rule during the rewrite) was removed as dead weight
once every section had a real heading, so each page drew its title
twice, the <h1> and an identical headline under it. The <h2>s are
md-visually-hidden again, the frame's comment says why, and the
section page test asserts it. The Layout section's description said
"window size classes"; M3's term is breakpoints.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

resources/views/showcase/section.blade.php

@@ -1,6 +1,6 @@
 {{-- One section of the showcase on a page of its own, with the way on to the next. The page's
-     heading names the section, so the section's own heading is only for a screen reader
-     (`data-md-showcase-sections`'s own rule in resources/css/showcase.css). --}}
+     heading names the section, so the section's own <h2> is `md-visually-hidden`: there for a
+     screen reader's outline of the <section>, not drawn a second time under the <h1>. --}}
 
 @extends('livewire-material::showcase.layout')
 
@@ -19,7 +19,7 @@
                 <h1 class="md-type-headline-lg">{{ $sections[$section]['title'] }}</h1>
             </x-livewire-material::stack>
 
-            <x-livewire-material::stack gap="space800" data-md-showcase-sections>
+            <x-livewire-material::stack gap="space800">
                 @include('livewire-material::showcase.sections.'.$section)
 
                 <x-livewire-material::stack gap="space300">