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>

app/Models/EmailTemplate.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Model;
+
+class EmailTemplate extends Model
+{
+    protected $fillable = ['key', 'label', 'subject', 'body', 'variables'];
+    protected $casts = ['variables' => 'array'];
+
+    public static function getByKey(string $key): ?self
+    {
+        return static::where('key', $key)->first();
+    }
+
+    public function renderBody(array $data): string
+    {
+        $body = $this->body;
+        foreach ($data as $k => $v) {
+            $body = str_replace('{{' . $k . '}}', (string) $v, $body);
+        }
+        return $body;
+    }
+
+    public function renderSubject(array $data): string
+    {
+        $subject = $this->subject;
+        foreach ($data as $k => $v) {
+            $subject = str_replace('{{' . $k . '}}', (string) $v, $subject);
+        }
+        return $subject;
+    }
+}

app/Models/Page.php

@@ -6,7 +6,7 @@ use Illuminate\Database\Eloquent\Model;
 
 class Page extends Model
 {
-    protected $fillable = ['slug','title','content','type','image','meta_title','meta_description','published','published_at','show_in_footer','show_in_nav','nav_sort'];
+    protected $fillable = ['slug','title','content','type','image','meta_title','meta_description','published','published_at','show_in_footer','show_in_nav','nav_sort','layout'];
 
     protected $casts = ['published' => 'boolean', 'published_at' => 'datetime', 'show_in_footer' => 'boolean', 'show_in_nav' => 'boolean'];
 }