Update docs/PROTOCOL_WS.md.
Include:
- •protocolVersion
- •message envelope (type, ts, requestId, tableId, seatToken, payload)
- •idempotency keys for action submission
- •replay protection strategy (monotonic seq per client or per seat)
- •error codes and retry rules
- •full example flows:
- •join -> ws connect -> start hand -> actions -> end hand
- •disconnect -> reconnect -> state resync