- Bump workspace version from 0.5.0 to 0.5.1
- Add mnemonic module with expand() function for BIP-39 word prefix expansion
- Implement prefix-based word completion (minimum 4 characters for unambiguous expansion)
- Add new error variants: PrefixTooShort, UnknownPrefix, AmbiguousPrefix
- Integrate mnemonic::expand() into Bitcoin, Ethereum, Solana, and mnemonic CLI commands
- Add comprehensive test coverage for expansion scenarios