Add M3 error pages and the Markdown mail theme

Error pages for 401 to 503 in an error-view root appended to view.paths,
with an inline fallback when the Vite build is missing, and a mail theme
rendered from the application's scheme JSON, with opt-in header and
message components. Completes Phase 9.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V9NnLxnPp8vaaurb3Z1MFy

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

@@ -0,0 +1,16 @@
+<section id="pages" class="scroll-mt-24 space-y-6">
+    <h2 class="type-headline-md">Pages</h2>
+
+    <p class="max-w-3xl type-body-md text-on-surface-variant">
+        The error pages, raised for real so an app's own <code>resources/views/errors</code> still wins, and the Markdown mail theme
+        (<code>livewire-material::mail.theme</code>) on a sample mail, both in this application's scheme.
+    </p>
+
+    <div class="flex flex-wrap items-center gap-2">
+        @foreach (['401', '402', '403', '404', '419', '429', '500', '503'] as $code)
+            <x-button :link="route('livewire-material.error', $code)" :label="$code" variant="tonal" no-wire-navigate />
+        @endforeach
+
+        <x-button :link="route('livewire-material.mail')" label="Sample mail" icon="mail" variant="outlined" no-wire-navigate />
+    </div>
+</section>