Add a search to the showcase

A search app bar looks through every section, example and component,
opens the section, or the example at its anchor on its page, and is
reached from anywhere with / or Ctrl+K. Section pages now carry their
own heading.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V9NnLxnPp8vaaurb3Z1MFy

tests/Feature/ShowcaseTest.php

@@ -45,6 +45,26 @@ it('gives every section a page of its own, linked from the overview and the rail
     $this->get('/material/not-a-section')->assertNotFound();
 });
 
+it('indexes every section, example and component for the search, each linking to a place that exists', function () {
+    $index = collect($this->getJson('/material/search.json')->assertOk()->json());
+
+    expect($index->where('kind', 'Section')->pluck('title')->all())
+        ->toBe(collect(Sections::all())->pluck('title')->all())
+        ->and($index->where('kind', 'Component')->pluck('title')->all())
+        ->toContain('<x-datepicker>', '<x-button>', '<x-app-shell>')
+        ->and($index->firstWhere('title', '<x-datepicker>')['url'])->toBe('/material/pickers');
+
+    $index->where('kind', 'Example')
+        ->groupBy(fn (array $entry): string => strtok($entry['url'], '#'))
+        ->each(function ($examples, string $page): void {
+            $html = $this->withoutVite()->get($page)->assertOk()->getContent();
+
+            foreach ($examples as $example) {
+                expect($html)->toContain('id="'.substr($example['url'], strpos($example['url'], '#') + 1).'"');
+            }
+        });
+});
+
 it('does not mount the showcase when disabled', function () {
     rebootWithShowcase(false);