Fix language persistence across navigation and breadcrumbs

- Add lang parameter to all navigation links in scanDirectory method
- Update homepage link in navigation template to include current language
- Fix breadcrumb navigation to preserve language parameter
- Ensure language selection persists when clicking any navigation element

engine/templates/assets/navigation.mustache

@@ -4,7 +4,7 @@
             <div class="col">
                 <ul class="nav nav-tabs flex-wrap">
 <li class="nav-item">
-                    <a class="nav-link {{home_active_class}}" href="?page={{homepage}}">
+                    <a class="nav-link {{home_active_class}}" href="?page={{homepage}}&lang={{current_lang}}">
                         <i class="bi bi-house"></i> {{homepage_title}}
                     </a>
                 </li>