sendFederatedCallStart now collects per-targeted-peer results and emits
a single dm_call_undeliverable event to the caller when any targeted
peer relay fails. Destroys the local ring room when no plausible
recipient remains (no targeted success + no connected local ringee).
LiveKit pre-flight also emits via this path with reason
'livekit_unavailable' instead of a silent console.warn, closing the
60s hang for unconfigured instances.
Guards against phantom toasts when the caller cancels mid-race by
checking getRoom() before emitting.
Jannis Braun
f83c2af357