v0.2.0 — transaction signing Adds Legacy + EIP-1559 transaction construction and signing via FFI to libsecp256k1 and libgmp. New modules: evm.bigint, evm.rlp, evm.secp256k1, evm.signer (replaces v0.1 stub), evm.transaction. Five new client methods for the signing workflow. Read-only v0.1 surface unchanged. Live broadcast verified on Sepolia: https://sepolia.etherscan.io/tx/0x201fe7e4ccefc902705244e9d14255d1bf076902ff41e3a682640c760f3f7ef7