v0.19.0 — the showcase release

The library learns to show itself — and stops calling itself production-grade.

• The live console — try it: the real engine compiled to WebAssembly matching a noise-trader market in your browser, with OFI/CVD/imbalance/Kyle-λ computed by the shipping pkg/signals code and pkg/surveillance watching every event. Every panel is titled by the exact library call that produces it. Place a limit order and watch it rest; run a spoof or a flood and watch the shipping detectors name the account. The market bar streams EngineSnapshot.Digest, so the determinism claim is falsifiable from the page.
• cmd/obdash — an operator dashboard that is deliberately an ordinary subscriber: the venue's own market-data wire plus its /metrics page, re-served over SSE. The venue gains no code, no port, no attack surface — and the protocol gets a consumer written from the format alone, outside its own test tree.
• "Production-grade" is retired from every header. Production readiness is a property of a deployment, not of code; no deployment exists, and independent review stands at none — so the headers now carry only what the tests can prove, and docs/PRODUCTION-READINESS.md carries the honest account. The docs page's stale benchmark figures (published for twelve releases) were caught and corrected in the same pass.

Full detail: CHANGELOG.md, docs/CONSOLE-SPEC.md.