feat(commands): add GenerateSitemapCommand for sitemap generation

- Added GenerateSitemapCommand to create sitemap.xml
- Updated Kernel to schedule sitemap generation weekly
- Updated composer.json with spatie/laravel-sitemap dependency

app/Console/Commands/GenerateSitemapCommand.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Console\Commands;
+
+use Illuminate\Console\Command;
+use Spatie\Sitemap\SitemapGenerator;
+
+class GenerateSitemapCommand extends Command
+{
+    protected $signature = 'sitemap:generate';
+
+    protected $description = 'Command description';
+
+    public function handle(): void
+    {
+        SitemapGenerator::create('https://heimerdinger.lol')
+            ->writeToFile(public_path('sitemap.xml'));
+    }
+}