Implements E2EE for relay connections only, keeping direct connections
and CLI plaintext. The relay acts as a dumb byte forwarder with no
access to decrypted messages.
Key changes:
- Daemon keypair persistence in $PASEO_HOME/daemon-keypair.json
- Encrypted relay transport using ECDH P-256 + AES-256-GCM
- Client-side E2EE using daemon's public key from pairing offer
- WebCrypto compatibility for React Native