docs: add inline documentation where missing

src/Security/Crypt.php

@@ -1,10 +1,19 @@
 <?php
 
+declare(strict_types=1);
+
 namespace App\Security;
 
 use Spatie\Crypto\Rsa\PrivateKey;
 use Spatie\Crypto\Rsa\PublicKey;
 
+/**
+ * RSA encryption/decryption utilities for secure credential storage.
+ *
+ * Uses asymmetric encryption to store BPN API passwords securely. Private key
+ * encrypts data for storage, public key decrypts for API calls. Also provides
+ * signing/verification for message integrity.
+ */
 class Crypt
 {
     public function __construct(private readonly string $path)