Add backend service for cryptographically secure random hash generation with the following features:
- Singleton HashGenerationService using crypto, crypto-js, and ethers
- Human-readable code formatting with custom character set avoiding ambiguous characters
- Batch generation with uniqueness verification
- Express API endpoints for generation, verification, and Merkle tree creation
- Authentication utilities for blockchain smart contract integration
- Comprehensive unit and integration tests

This implementation moves secure hash generation from frontend to backend for improved security and auditability. All tests are passing and the API is ready for frontend integration.