v0.1.8 - Signed transaction and hot-path hardening

Adds optional minTipSol decimal SOL thresholds and filters ineligible provider lanes before building, signing or sending. Hardens deadlines, blockhash/nonce lifecycle, cache selection and transfer-fee rounding. Uses native Ed25519 for V1 signing with signer validation and immutable message snapshots; adds signed wire and ALT regressions.

Validation includes local CPU benchmarks and offline signed-bank scenarios. Measured hot paths use cached inputs without RPC. Benchmarks do not establish production network or transaction-landing latency. No funded mainnet transactions were broadcast.

Package registry status: published to npm as sol-trade-sdk@0.1.8. The registry integrity matches the tested tarball attached to this release.