Implement dynamic language system with automatic detection

- Add getAvailableLanguages() method to scan lang directory automatically
- Add getNativeLanguageName() method for proper language display names
- Enhance SimpleTemplate engine to support array iteration with {{#array}} syntax
- Update header template to use dynamic language dropdown with native names
- Add German (de.php) and French (fr.php) language files as examples
- Fix search input text color to use black text for better visibility
- Languages now appear automatically when added to engine/lang/ without code changes

engine/templates/assets/header.mustache

@@ -18,8 +18,9 @@
                     {{current_lang_upper}} <i class="bi bi-chevron-down"></i>
                 </button>
                 <ul class="dropdown-menu dropdown-menu-end">
-                    <li><a class="dropdown-item" href="?lang=nl{{lang_switch_url}}">NL</a></li>
-                    <li><a class="dropdown-item" href="?lang=en{{lang_switch_url}}">EN</a></li>
+                    {{#available_langs}}
+                    <li><a class="dropdown-item {{#is_current}}active{{/is_current}}" href="?lang={{code}}{{lang_switch_url}}">{{native_name}}</a></li>
+                    {{/available_langs}}
                 </ul>
             </div>
         </div>
@@ -33,8 +34,9 @@
                 {{current_lang_upper}} <i class="bi bi-chevron-down"></i>
             </button>
             <ul class="dropdown-menu dropdown-menu-end">
-                    <li><a class="dropdown-item" href="?lang=nl{{lang_switch_url}}">NL</a></li>
-                    <li><a class="dropdown-item" href="?lang=en{{lang_switch_url}}">EN</a></li>
+                    {{#available_langs}}
+                    <li><a class="dropdown-item {{#is_current}}active{{/is_current}}" href="?lang={{code}}{{lang_switch_url}}">{{native_name}}</a></li>
+                    {{/available_langs}}
             </ul>
         </div>
     </div>