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

tests/Pest.php

@@ -4,6 +4,21 @@ use NoNameWeb\LivewireMaterial\Tests\TestCase;
 
 pest()->extend(TestCase::class)->in('Feature', 'Browser');
 
+/**
+ * The element name (under `<`) and the attributes of the first tag in a rendered component, by
+ * name; a boolean attribute Blade renders as `name="name"`. For the layout components' render
+ * tests, which assert what their root carries.
+ *
+ * @return array<string, string>
+ */
+function layoutRoot(string $html): array
+{
+    preg_match('/^\s*<([a-z]+)\b([^>]*)>/s', $html, $tag);
+    preg_match_all('/([\w:.@-]+)(?:="([^"]*)")?/', $tag[2] ?? '', $pairs, PREG_SET_ORDER);
+
+    return ['<' => $tag[1] ?? ''] + collect($pairs)->mapWithKeys(fn (array $pair): array => [$pair[1] => $pair[2] ?? ''])->all();
+}
+
 // A shared CI runner is slower than a workstation: an animation or a smooth scroll can take longer
 // than the default five seconds to settle there. BROWSER_TIMEOUT (milliseconds) raises the limit.
 if (($timeout = (int) getenv('BROWSER_TIMEOUT')) > 0) {