Write the showcase examples' layout tags as an application does

Plan step 38 review: nine sections' examples wrapped their components
in <x-livewire-material::stack>, ::row and ::grid (148 tags) beside an
unprefixed <x-button>, while bars, containment and the layout pages
wrote <x-stack>. The code sample is what an application copies, and
the example component rewrites only unprefixed tags to a configured
prefix, so the namespaced ones taught a second form and escaped it.
Every example now writes <x-stack>, <x-row> and <x-grid>; a test
rejects a namespaced tag inside an example heredoc.

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

tests/Feature/ShowcaseTest.php

@@ -117,6 +117,25 @@ it('indexes exactly the examples each page renders, so an example the index miss
     }
 });
 
+it('writes every example as an application writes it', function () {
+    $files = collect(File::glob(__DIR__.'/../../resources/views/showcase/sections/*.blade.php'))
+        ->merge(File::glob(__DIR__.'/../../resources/views/showcase/layout/*.blade.php'));
+
+    $examples = $files->flatMap(function (string $file): array {
+        preg_match_all("/<<<'BLADE'\n(.*?)^\s*BLADE[,;]/sm", File::get($file), $matches);
+
+        return array_map(fn (string $code): array => [basename($file), $code], $matches[1]);
+    });
+
+    expect($examples)->not->toBeEmpty();
+
+    foreach ($examples as [$file, $code]) {
+        // The example component rewrites unprefixed tags to a configured prefix; a namespaced tag
+        // would show an application a form it does not write, and escape that rewrite.
+        expect($code)->not->toContain('x-livewire-material::', "{$file} writes a namespaced tag in an example");
+    }
+});
+
 it('does not mount the showcase when disabled', function () {
     rebootWithShowcase(false);