feat: core utilities - CSRF, auth, encryption, PHPMailer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

includes/encryption.php

@@ -0,0 +1,17 @@
+<?php
+require_once __DIR__ . '/config.php';
+
+function encryptData(string $plaintext): string {
+    $iv = random_bytes(16);
+    $key = hash('sha256', ENCRYPTION_KEY, true);
+    $encrypted = openssl_encrypt($plaintext, 'aes-256-cbc', $key, OPENSSL_RAW_DATA, $iv);
+    return base64_encode($iv . $encrypted);
+}
+
+function decryptData(string $ciphertext): string {
+    $data = base64_decode($ciphertext);
+    $iv = substr($data, 0, 16);
+    $encrypted = substr($data, 16);
+    $key = hash('sha256', ENCRYPTION_KEY, true);
+    return openssl_decrypt($encrypted, 'aes-256-cbc', $key, OPENSSL_RAW_DATA, $iv);
+}