feat(lotus): io.lotus.set_audio_output — host-driven output device switch (#119)

The embed hides Element Call's footer, so its own output picker is out of
reach; the host's call bar now sends io.lotus.set_audio_output { deviceId }
and the fork applies it via mediaDevices.audioOutput.select(), answering
with io.lotus.audio_output_state { deviceId } on every change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/lotus/lotusActions.test.ts

@@ -26,6 +26,7 @@ describe("LotusWidgetActions", () => {
       LotusWidgetActions.SetQuality,
       LotusWidgetActions.Decorations,
       LotusWidgetActions.SetDeafen,
+      LotusWidgetActions.SetAudioOutput,
     ];
 
     expect(new Set(LOTUS_TO_WIDGET_ACTIONS)).toEqual(new Set(expectedToWidget));