Join the team's live reception switchboard over WebSocket

Upgrade to WebSocket on the same origin. Within five seconds send TelephonyClientMessage kind authenticate with a GP-scoped team API key and receptionist name. Credentials never belong in the URL. The server assigns a memberId and broadcasts TelephonyServerMessage snapshots scoped to that world. Send command messages with unique requestId values; use the current call version for claims, hold, transfer, callback, end and end-and-next. Acknowledgements include requestId. Reuse a requestId only for the same command. Reconnect by authenticating again; calls held by a disconnected member return to the queue. Phone timestamps use wall-clock milliseconds, independent of simulation speed. HTTP clients without a WebSocket upgrade receive 426.