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/mail/html/header.blade.php

@@ -0,0 +1,24 @@
+{{-- The mail's masthead: the app name in title-lg, or the logo from
+     `livewire-material.mail.logo` (`src`, `width`, `height`).
+
+     Replaces the framework's header, which swaps the name for Laravel's own logo whenever the
+     app is still called "Laravel". A logo keeps the name as its alt text, for readers with
+     images off; its width and height are repeated as attributes because Outlook sizes an image
+     from those and ignores the stylesheet. Serve the file at twice those dimensions to stay
+     crisp, from an absolute URL — a queued mail has no request to resolve a relative one. --}}
+@props(['url', 'logo' => config('livewire-material.mail.logo')])
+@php
+    $name = trim(strip_tags((string) $slot));
+    $src = is_array($logo) ? ($logo['src'] ?? null) : null;
+@endphp
+<tr>
+<td class="header">
+<a href="{{ $url }}" style="display: inline-block;">
+@if (filled($src))
+<img src="{{ $src }}" class="logo" alt="{{ $name }}" @if (filled($logo['width'] ?? null)) width="{{ $logo['width'] }}" @endif @if (filled($logo['height'] ?? null)) height="{{ $logo['height'] }}" @endif style="border: 0;">
+@else
+{{ $name }}
+@endif
+</a>
+</td>
+</tr>