State 016 acceptance harness

Estate-owned headless E2E coverage for the offline acceptance flow (10 gates, see ../README.md). Not FINOS-upstream: it assumes headless Chrome and local tooling. The manual acceptance script a maintainer needs is ../../acceptance-demo.md — this harness only automates proving it.

# 1. Serve the spec pack (repo root):
python3 -m http.server 8090 --directory specs/016-post-trade-settlement-bankerx

# 2. Install + run the harness (Chrome executable overridable via CHROME_EXE):
cd specs/016-post-trade-settlement-bankerx/acceptance/harness
npm install
node acceptance-016.cjs http://localhost:8090 clean-run

Gates: realFdc3, deskOpen, wcpConnected, tradeBooked, intentReceived, acsc, receiptModal, dupSuppressed, receiverDupReplay, rejectHonest. Exit code 0 iff all 10 pass. On failure it dumps filtered console evidence.