lotus(#6): render avatar decorations on in-call tiles

Adds io.lotus.decorations (toWidget): the host pushes a userId->image-URL
map and EC overlays the profile decoration on each tile avatar
(TileAvatar), keyed by userId, with a useSyncExternalStore-backed store.
Makes A6 first-class in-call instead of absent. URLs are validated
https/blob. Additive: no-op unless the host sends decorations.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/room/InCallView.tsx

@@ -33,6 +33,7 @@ import { startLotusCallState } from "../lotus/lotusCallState";
 import { startLotusFocus } from "../lotus/lotusFocus";
 import { startLotusAudioInject } from "../lotus/lotusAudioInject";
 import { startLotusQuality } from "../lotus/lotusQuality";
+import { startLotusDecorations } from "../lotus/lotusDecorations";
 import styles from "./InCallView.module.css";
 import { GridTile } from "../tile/GridTile";
 import { SettingsModal, defaultSettingsTab } from "../settings/SettingsModal";
@@ -295,6 +296,9 @@ export const InCallView: FC<InCallViewProps> = ({
   // [lotus] Handle the host's io.lotus.set_quality action to cap audio/
   // screenshare encoding bitrate/framerate (#7). No-op unless the host sends it.
   useEffect(() => startLotusQuality(vm), [vm]);
+  // [lotus] Receive per-user avatar-decoration URLs from the host and render
+  // them on in-call tile avatars (#6). No-op unless the host sends them.
+  useEffect(() => startLotusDecorations(), []);
 
   const fatalCallError = useBehavior(vm.fatalError$);
   // Stop the rendering and throw for the error boundary