- Add relay_seckey table for secure private key storage
- Implement store_relay_private_key() and get_relay_private_key() functions
- Remove relay private key from public configuration events (kind 33334)
- Update first-time startup sequence to store keys securely after DB init
- Add proper validation and error handling for private key operations
- Fix timing issue where private key storage was attempted before DB initialization
- Security improvement: relay private keys no longer exposed in public events
