feat(lotus): io.lotus.screenshare_notice — window closed, no frames, sharing alone (#39)

Watches the local screenshare publication and tells the host, once per
share each: the MediaStreamTrack ended (window closed), it has been muted
(no frames — minimised/occluded window) for 15 s, or 30 min of sharing
with nobody else in the call. Detection only; the host renders the
notices. LiveKit already unpublishes an ended share, so nothing lingers.

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

src/room/InCallView.tsx

@@ -37,6 +37,7 @@ import { startLotusDecorations } from "../lotus/lotusDecorations";
 import { startLotusDenoise } from "../lotus/lotusDenoise";
 import { startLotusCallSummary } from "../lotus/lotusCallSummary";
 import { startLotusAudioOutput } from "../lotus/lotusAudioOutput";
+import { startLotusScreenshareWatch } from "../lotus/lotusScreenshareWatch";
 import { startLotusDeafen } from "../lotus/lotusDeafen";
 import styles from "./InCallView.module.css";
 import { GridTile } from "../tile/GridTile";
@@ -312,6 +313,8 @@ export const InCallView: FC<InCallViewProps> = ({
   // survives reconnects (#1 / A7). No-op unless lotusDenoiseSource=1.
   useEffect(() => startLotusDenoise(vm), [vm]);
   useEffect(() => startLotusCallSummary(vm), [vm]);
+  // [lotus #39] Screenshare reminders (window closed / black / sharing alone).
+  useEffect(() => startLotusScreenshareWatch(vm), [vm]);
   // [lotus] Handle the host's io.lotus.set_deafen action to silence remote
   // audio (and optionally screenshare audio) at the LiveKit source. No-op
   // unless the host sends the action.