fix(phase-1): resolve preloader freeze, lock dark mode, perfectly center hamburger & mark complete

helpers.php

@@ -216,3 +216,16 @@ function lang_url(string $lang): string {
     $path = strtok($_SERVER['REQUEST_URI'], '?') ?: '/';
     return $path . '?' . http_build_query($params);
 }
+
+// Fallback polyfills for environments without mbstring extension
+if (!function_exists('mb_substr')) {
+    function mb_substr(string $string, int $start, ?int $length = null, ?string $encoding = null): string {
+        return substr($string, $start, $length ?? strlen($string));
+    }
+}
+
+if (!function_exists('mb_strlen')) {
+    function mb_strlen(string $string, ?string $encoding = null): int {
+        return strlen($string);
+    }
+}