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

routes/showcase.php

@@ -20,6 +20,8 @@ Route::get('errors/{code}', [ShowcasePageController::class, 'error'])
     ->name('error');
 Route::get('mail', [ShowcasePageController::class, 'mail'])->name('mail');
 
+Route::get('search.json', [ShowcaseController::class, 'search'])->name('search');
+
 Route::get('{section}', [ShowcaseController::class, 'section'])
     ->whereIn('section', array_keys(Sections::all()))
     ->name('section');