Add the stack layout component and the layout foundation

Plan step 35: <x-stack gap align>, the first of M3's layout components,
with what they all share - src/Support/Layout.php reading the props into
data-md-* attributes, the spacing-token gap and padding rules, the
hide-below/hide-from rules in material.visibility, the stylesheet checks
for resources/css/layout, the browser test file and the skill's Layout
group. The Workbench puts the material layers above Tailwind's preflight,
which would otherwise zero every layout padding and margin.

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

@@ -102,4 +102,18 @@
         content margin (<code>--material-margin</code>) change at 600, 840 and 1200px. A visitor who has chosen a rail
         width keeps it; until then the rail follows the class.
     </p>
+
+    <x-livewire-material::stack gap="space200" data-test="layout-components">
+        <h3 class="md-type-title-lg">The layout components</h3>
+
+        <p class="md-type-body-md md-ink-variant">
+            M3 describes a layout as a scaffold of bars and rails around panes, and names three canonical layouts. These are
+            those words as components, each taking <code>as</code>, <code>hide-below</code> and <code>hide-from</code>, and
+            only the spacing tokens for a gap or padding:
+        </p>
+
+        <x-livewire-material::stack as="ul" gap="space100" class="md-type-body-md">
+            <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>
+    </x-livewire-material::stack>
 </section>