Add email templates, page layouts, and shop themes (template system)

- E-Mail-Templates: DB-gespeicherte HTML-Templates mit {{placeholder}}-System,
  Admin-UI zum Bearbeiten von Betreff und Body, alle 4 Mailables aktualisiert
- Seiten-Layouts: 4 Layouts für CMS-Seiten (Standard, Sidebar, Volle Breite, Landing),
  Layout-Auswahl im Admin-Formular
- Shop-Themes: 5 Farbthemen via CSS-Variablen, Picker in Einstellungen
- Deployment: EmailTemplateSeeder wird automatisch beim Deploy ausgeführt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

resources/views/shop/page.blade.php

@@ -1,11 +1,59 @@
+@php $layout = $page->layout ?? 'default'; @endphp
+
+@if($layout === 'landing')
+<!DOCTYPE html>
+<html lang="de">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>{{ $page->meta_title ?: $page->title }}</title>
+    <meta name="description" content="{{ $page->meta_description }}">
+    @vite(['resources/css/app.css', 'resources/js/app.js'])
+</head>
+<body class="bg-gray-50 text-gray-800">
+    <div class="prose max-w-none text-gray-700 p-8">
+        {!! $page->content !!}
+    </div>
+</body>
+</html>
+@else
 @extends('layouts.shop')
 @section('title', $page->meta_title ?: $page->title)
 @section('meta_description', $page->meta_description)
 @section('content')
-<div class="max-w-3xl mx-auto">
+
+@switch($layout)
+
+    @case('full')
     <h1 class="text-3xl font-bold mb-6">{{ $page->title }}</h1>
     <div class="prose max-w-none text-gray-700">
         {!! $page->content !!}
     </div>
-</div>
+    @break
+
+    @case('sidebar')
+    <div class="grid grid-cols-1 lg:grid-cols-3 gap-8">
+        <div class="lg:col-span-2">
+            <h1 class="text-3xl font-bold mb-6">{{ $page->title }}</h1>
+            <div class="prose max-w-none text-gray-700">
+                {!! $page->content !!}
+            </div>
+        </div>
+        <aside class="space-y-6">
+            @include('shop.partials._sidebar')
+        </aside>
+    </div>
+    @break
+
+    @default
+    <div class="max-w-3xl mx-auto">
+        <h1 class="text-3xl font-bold mb-6">{{ $page->title }}</h1>
+        <div class="prose max-w-none text-gray-700">
+            {!! $page->content !!}
+        </div>
+    </div>
+
+@endswitch
+
 @endsection
+@endif