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/boost/skills/livewire-material-development/SKILL.md

@@ -85,6 +85,59 @@ class Settings extends Component
 
 The methods are protected. They dispatch a `toast` browser event (`assertDispatched('toast', type: 'success', title: 'Settings saved')` in tests).
 
+## Error pages
+
+Laravel's HTTP error pages — 403, 404, 419, 429, 500, 503, and the framework's own 401 and 402 — render in M3 without setup. The provider appends the package's error views to `view.paths` after the application's, so a file in `resources/views/errors/` always wins.
+
+- The pages load `config('livewire-material.showcase.vite')` and `<x-theme-script />`, so they use the app's scheme, font and theme. While the build is missing (a deploy in progress) they fall back to an inline stylesheet coloured from `resources/css/material-scheme.json`.
+- `abort(403, 'Only the owner can open this share.')` and `abort(503, '…')` show the message as the sentence. Every other string goes through `__()`; translate them in `lang/{locale}.json`.
+- To change wording or design, run `php artisan vendor:publish --tag=livewire-material-errors`, which copies the layout and pages to `resources/views/errors`. A page extends `errors::minimal` and sets `title`, `code`, `headline`, `message`, `shape` (an `<x-shape>` name) and optionally `actions`:
+
+```blade
+@extends('errors::minimal')
+
+@section('title', __('Payment Required'))
+@section('code', '402')
+@section('shape', 'cookie-4')
+@section('headline', __('Your plan has ended'))
+@section('message', __('Choose a plan to keep using the app.'))
+
+@section('actions')
+    <x-button :link="route('billing')" :label="__('Choose a plan')" variant="filled" size="md" no-wire-navigate />
+@endsection
+```
+
+- Maintenance mode: `php artisan down --render="errors::503"`.
+- The showcase previews each page at `/material/errors/{code}`.
+
+## Mail
+
+Markdown mail (notifications and `markdown:` mailables) wears M3 once the application selects the theme:
+
+```dotenv
+MAIL_MARKDOWN_THEME=livewire-material::mail.theme
+```
+
+or per mail: `(new MailMessage)->theme('livewire-material::mail.theme')`, or `public $theme = 'livewire-material::mail.theme';` on a mailable.
+
+- Colours are the light scheme from `resources/css/material-scheme.json` (`livewire-material.scheme`), inlined as hexes; regenerate the scheme and mail follows. Without the file, the package's default scheme applies.
+- Write the body as Markdown; the theme styles the bare tags (`#` headings, prose, lists, tables) with M3's typescale. `<x-mail::button :url="…">` is a filled pill in `primary`; `color` also takes `secondary`, `tertiary`, `error`, `success`, `warning` and `info`. `<x-mail::panel>` is a tinted container.
+- There is no dark mail. Never put `@media` rules, CSS variables or `color-mix()` in mail CSS: the inliner strips media queries and mail clients resolve no variables.
+- The package's mail header (the app name, or a logo) and message (with a replaceable footer) are opt-in: set `MATERIAL_MAIL_COMPONENTS=true`, or `php artisan vendor:publish --tag=livewire-material-mail` to copy them into `resources/views/vendor/mail`. For a logo set `livewire-material.mail.logo` to `['src' => 'https://example.com/logo.png', 'width' => 160, 'height' => 40]`: an absolute URL, with the image at twice those dimensions.
+- With those components, a mail can replace the footer:
+
+```blade
+<x-mail::message>
+Your export is ready.
+
+<x-slot:footer>
+© {{ date('Y') }} {{ config('app.name') }} · [Unsubscribe]({{ $unsubscribeUrl }})
+</x-slot:footer>
+</x-mail::message>
+```
+
+- The showcase renders a sample mail at `/material/mail`.
+
 ## Components
 
 ### `<x-icon>`