feat(lotus): layout, settings and reactions over the widget API (cinny #43)

The Lotus host drove these by clicking EC's hidden controls in our DOM and
read screenshare/layout state from it, which only works while the frame is
same-origin and breaks whenever a data-testid changes. New actions:

- toWidget io.lotus.set_layout { layout: "grid" | "spotlight" } → the layout
  switch view model's setLayout.
- toWidget io.lotus.open_settings { open?: boolean } → setSettingsOpen
  (toggle when `open` is omitted).
- toWidget io.lotus.toggle_reactions → a window event the reactions button
  listens for.
- fromWidget io.lotus.controls_state { screensharing, layout } on change; its
  arrival tells the host the fork supports the actions above.

Screensharing stays host-driven for now: getDisplayMedia needs the user's
click to reach this frame (Capability Delegation), which a widget message
doesn't carry.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/room/InCallView.tsx

@@ -31,6 +31,7 @@ import { useCallViewKeyboardShortcuts } from "../useCallViewKeyboardShortcuts";
 import { widget } from "../widget";
 import { startLotusCallState } from "../lotus/lotusCallState";
 import { startLotusFocus } from "../lotus/lotusFocus";
+import { startLotusControls } from "../lotus/lotusControls";
 import { startLotusAudioInject } from "../lotus/lotusAudioInject";
 import { startLotusQuality } from "../lotus/lotusQuality";
 import { startLotusDecorations } from "../lotus/lotusDecorations";
@@ -300,6 +301,9 @@ export const InCallView: FC<InCallViewProps> = ({
   // [lotus] Handle the host's io.lotus.focus_participant action to pin a
   // participant to the spotlight (#4). No-op unless the host sends it.
   useEffect(() => startLotusFocus(vm), [vm]);
+  // [cinny #43] layout / settings / reactions over the widget API, plus a
+  // screensharing + layout report, replacing the host's DOM access.
+  useEffect(() => startLotusControls(vm), [vm]);
   // [lotus] Handle the host's io.lotus.inject_audio action to mix a soundboard
   // clip into the call as a separate track (#3). No-op unless the host sends it.
   useEffect(() => startLotusAudioInject(vm), [vm]);