v0.0.14: Ethereum-compatible identity (secp256k1 + Keccak-256)

Protocol (ethereum.rs):
- derive_eth_identity(): HKDF from seed (info="warzone-secp256k1")
- secp256k1 signing key (k256 crate)
- Ethereum address: Keccak-256(uncompressed_pubkey[1..])[-20:]
- EIP-55 checksum address formatting
- eth_sign() / eth_verify() for secp256k1 ECDSA
- EthAddress type with Display, hex parsing, checksum
- 5 tests: deterministic, format, checksum, sign/verify, uniqueness

CLI:
- `warzone eth` — show Ethereum address alongside Warzone fingerprint
- Same seed produces both identities (dual-curve)

Dual identity model:
- Ed25519 + X25519 for Warzone messaging (fast, small signatures)
- secp256k1 for Ethereum compatibility (MetaMask, ENS, Ledger/Trezor)
- Both derived from the same BIP39 seed via different HKDF paths

28/28 protocol tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

warzone/crates/warzone-protocol/Cargo.toml

@@ -21,3 +21,5 @@ base64.workspace = true
 uuid.workspace = true
 zeroize.workspace = true
 chrono.workspace = true
+k256.workspace = true
+tiny-keccak.workspace = true