fix: Disable close_on_disconnect to keep session alive

E2EE key setup may briefly appear as participant disconnect.
Keep session alive to allow audio to flow once keys are settled.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

voice.py

@@ -290,7 +290,8 @@ class VoiceSession:
             agent = Agent(instructions=VOICE_PROMPT)
             io_opts = room_io.RoomOptions(
                 participant_identity=remote_identity,
-            ) if remote_identity else room_io.RoomOptions()
+                close_on_disconnect=False,
+            ) if remote_identity else room_io.RoomOptions(close_on_disconnect=False)
             await self.session.start(
                 agent=agent,
                 room=self.lk_room,