Announce a selectable list as M3's list box of options

Plan step 12, containment.md C-03. `selected` was colour alone on a
`listitem`, which cannot carry a selected state at all. `<x-list
selectable>` (or `selection="single|multi"`) now makes the container a
`role="listbox"` and each item an `option` with `aria-selected`; a plain
list keeps `role="list"` and marks a selected item `aria-current`. A
selected option draws a trailing check as M3's second cue, which
`icon-right` replaces. The item reads its list's mode with `@aware`.

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

resources/views/showcase/sections/containment.blade.php

@@ -40,9 +40,17 @@
                     <x-list-item title="Chiara Rossi" avatar="CR">
                         <x-slot:end><x-button icon="more_vert" tooltip="More" /></x-slot:end>
                     </x-list-item>
+                    <x-list-item title="Dan Fischer" description="Invitation withdrawn" avatar="DF" link="#containment" disabled />
                 </x-list>
             </div>
             BLADE,
+        'A list to choose from' => <<<'BLADE'
+            <x-list selectable label="Expiry" class="w-full max-w-sm">
+                <x-list-item title="One hour" :selected="false" />
+                <x-list-item title="Three days" :selected="true" />
+                <x-list-item title="Thirty days" :selected="false" />
+            </x-list>
+            BLADE,
         'Dividers and collapse' => <<<'BLADE'
             <div class="w-full space-y-4">
                 <x-collapse title="How long do links last?" icon="schedule" open>