Add the feed canonical layout

Plan step 35: <x-feed min-item gap>, following the reference's feed rules
- one column below medium, then as many equal columns of at least the
minimum item width as the feed has room for, 24px apart from medium,
items in their source order.

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

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

@@ -116,6 +116,7 @@
             <li><code>&lt;x-pane&gt;</code> — a content region with M3's margins and its own app bar.</li>
             <li><code>&lt;x-list-detail&gt;</code> — a list and the detail of its selection: one pane below 840px, two from it.</li>
             <li><code>&lt;x-supporting-pane&gt;</code> — a focus pane and a pane beside it from 840px, below it or a bottom sheet before.</li>
+            <li><code>&lt;x-feed&gt;</code> — cards in columns that multiply as the room grows, one column below 600px.</li>
             <li><code>&lt;x-surface&gt;</code> — a tonal region: a surface role, padding, a corner and an outline.</li>
             <li><code>&lt;x-stack&gt;</code>, <code>&lt;x-row&gt;</code> and <code>&lt;x-grid&gt;</code> — arrangement inside a pane.</li>
         </x-livewire-material::stack>