- Add src/crypto.py with AES-256-CBC pw_encode/pw_decode
using double SHA256 key derivation (Electrum standard)
- Add encrypt_wallet() and decrypt_wallet() to src/hd_wallet.py
- Prompt for encryption password when saving HD wallet to file
- Add 13 encryption/decryption tests to tests/test_hd_wallet.py
- Add pycryptodome to requirements.txt
- Add pytest test suite for all 5 address types (P2PK, P2PKH, P2SH, P2WPKH, P2TR)
- Test output fields, address prefixes per network, key lengths and uniqueness
- Each test file prints the SecretScan URL for manual address verification
- Add pytest to requirements.txt
