Put the showcase in the app shell, with a page per section

The showcase is now an overview and one page per section behind a
grouped navigation rail, moved between with wire:navigate, instead of
one long page under a scrolling top bar. The switch exposed a WebKit
bug in the menu: inside a focusable region, WebKit moves focus out of
the closing popover before its toggle event, so Escape no longer
returned focus to the trigger. The menu now reads it on beforetoggle.

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

tests/Browser/ChipsTest.php

@@ -74,7 +74,7 @@ function chipProbe()
 
 function chipShowcase()
 {
-    return visit('/material')->waitForEvent('networkidle')
+    return visit('/material/chips')->waitForEvent('networkidle')
         ->assertScript("document.readyState === 'complete' && typeof window.Alpine !== 'undefined' && typeof window.Livewire !== 'undefined'");
 }
 
@@ -99,7 +99,7 @@ it('toggles a filter chip with a click and with Space, and grows its check in',
 
     // A key press first, so the browser is in keyboard modality; focused directly, not tabbed to,
     // because WebKit leaves form controls out of the Tab order unless full keyboard access is on.
-    $page->keys('body', 'Tab');
+    $page->keys('#content', 'Tab');
     $page->script(filterInput('archives').'.focus()');
     $page->keys(':focus', 'Space')
         ->assertScript(filterInput('archives').'.checked')