feat: implement CryptoModule with comprehensive cryptographic utilities and testing

Added CryptoModule providing services for Argon2 hashing, JWT handling, JWE encryption/decryption, JWS signing/verification, and post-quantum cryptography (ML-KEM). Includes extensive unit tests for all features.

backend/src/crypto/crypto.module.ts

@@ -0,0 +1,8 @@
+import { Module } from "@nestjs/common";
+import { CryptoService } from "./crypto.service";
+
+@Module({
+	providers: [CryptoService],
+	exports: [CryptoService],
+})
+export class CryptoModule {}