Refactor number formatting in landing page for improved localization support

- Updated the number formatting logic in index.php to enhance localization handling for German and English.
- Introduced variables for decimal and thousands separators based on the user's locale, ensuring accurate number representation.

landingpage/index.php

@@ -43,7 +43,9 @@ $formatNumber = static function (int $value) use ($numberLocale): string {
             return $formatted;
         }
     }
-    return number_format($value, 0, $locale === 'de' ? ',' : '.', $locale === 'de' ? '.' : ',');
+    $decimal = $numberLocale === 'de_DE' ? ',' : '.';
+    $thousands = $numberLocale === 'de_DE' ? '.' : ',';
+    return number_format($value, 0, $decimal, $thousands);
 };
 
 /** @var array<string, array{label: string, modules: list<array{label: string, description: string}>}> $groups */