fix: PSR-4 compliance — rename core/middleware/services to PascalCase for Linux server compatibility

app/Core/Validator.php

@@ -0,0 +1,25 @@
+<?php
+/**
+ * Simple Data Validator
+ */
+
+declare(strict_types=1);
+
+namespace App\Core;
+
+final class Validator
+{
+    public static function validate(array $data, array $rules): array
+    {
+        $errors = [];
+        foreach ($rules as $field => $rule) {
+            if (str_contains($rule, 'required') && (empty($data[$field]) && $data[$field] !== '0')) {
+                $errors[$field] = "The {$field} field is required.";
+            }
+            if (str_contains($rule, 'email') && !empty($data[$field]) && !filter_var($data[$field], FILTER_VALIDATE_EMAIL)) {
+                $errors[$field] = "The {$field} must be a valid email address.";
+            }
+        }
+        return $errors;
+    }
+}