fix: replace custom autoloader with composer PSR-4 autoloader

The custom autoloader used lowercase directory names which broke
after renaming app/core/ → app/Core/ and app/controllers/ → app/Controllers/
for PSR-4 compliance.

public/index.php

@@ -7,28 +7,8 @@ declare(strict_types=1);
  * All requests are routed through this file.
  */
 
-// Autoloader (PSR-4 style, simple)
+// Autoloader (composer PSR-4)
-spl_autoload_register(function (string $class): void {
+require_once __DIR__ . '/../vendor/autoload.php';
-    $prefix = 'App\\';
-    $baseDir = __DIR__ . '/../app/';
-
-    $len = strlen($prefix);
-    if (strncmp($prefix, $class, $len) !== 0) {
-        return;
-    }
-
-    $relativeClass = substr($class, $len);
-    // Lowercase directory names, keep class name case
-    $parts = explode('\\', $relativeClass);
-    $className = array_pop($parts);
-    $parts = array_map('strtolower', $parts);
-    $parts[] = $className;
-    $file = $baseDir . implode('/', $parts) . '.php';
-
-    if (file_exists($file)) {
-        require $file;
-    }
-});
 
 use App\Core\Router;