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/error-pages/errors/419.blade.php

@@ -0,0 +1,16 @@
+{{-- Page expired: the form's CSRF token outlived the session. Reloading the page the form was on
+     issues a new one, so that is the action — a link to it, never a reload of this response,
+     which would post the stale form again. --}}
+
+@extends('errors::minimal')
+
+@section('title', __('Page Expired'))
+@section('code', '419')
+@section('shape', 'clover-4')
+@section('headline', __('This page has expired'))
+@section('message', __('It was open for a while. Refresh it, then try again.'))
+
+@section('actions')
+    <x-button :link="url()->previous()" :label="__('Refresh the page')" variant="filled" size="md" no-wire-navigate />
+    <x-button :link="url('/')" :label="__('Go home')" variant="text" size="md" no-wire-navigate />
+@endsection