Two-pronged fix for the race between GatewayReady auto-creating a session
and ChatScreen LaunchedEffect calling switchSession:
1. ChatViewModel: added `initialSessionId` field. GatewayReady now checks
this before auto-creating a session — if set, it calls switchSession
instead. The field is set synchronously by ChatScreen via SideEffect
during composition, before any WS event can be processed.
2. ChatScreen: LaunchedEffect now keys on state.connectionStatus and
waits for CONNECTED before calling switchSession. This prevents the
SESSION_RESUME message from being dropped (webSocket is null before
onOpen, so send() is a silent no-op).
Fixes#240
Co-authored-by: M57 <hy4ri@users.noreply.github.com>
