Add the supporting-pane canonical layout

Plan step 35: <x-supporting-pane>, following the reference's placement
table - below the focus pane below expanded, beside it from 840px at a
fixed 360px (412px from large) or the two-thirds split. Below expanded
compact="sheet" docks the supporting pane as a bottom sheet whose drag
handle opens it; always on the trailing side, so focus order matches the
panes on screen, and mirrored in RTL.

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

@@ -115,6 +115,7 @@
         <x-livewire-material::stack as="ul" gap="space100" class="md-type-body-md">
             <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-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>