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

src/scss/main.scss

@@ -271,12 +271,12 @@ footer {
   max-width: 300px;
 }
 
-/* Search input text color */
-.search-input {
-  color: #212529 !important;
+/* Search input text color - override navbar form-control styling */
+.navbar .form-control.search-input {
+  color: #000000 !important;
 }
 
-.search-input::placeholder {
+.navbar .form-control.search-input::placeholder {
   color: #6c757d !important;
 }