Hoist usePollSubscriptions to RoomWidgetsView; drop the side effect from usePollWidget

Follow-up to the previous commit's poll split. The compat shim
usePollWidget used to call usePollSubscriptions() inside its body so
the three RoomSessionPollEvent listeners were still registered for
existing consumers — but that meant:
- listeners would be re-registered per consumer (today nobody, since
  useWordQuizWidget was already migrated to usePollActions);
- the lifetime of the subscriptions was tied to a leaf widget instead
  of the room session;
- a render of a component using the shim had the side effect of
  attaching three global event listeners.

Move
- src/components/room/widgets/RoomWidgetsView.tsx now calls
  usePollSubscriptions() once at the top of the room-widget tree. The
  bridge from RoomSessionPollEvent (OFFER/ERROR/CONTENT) to the UI
  event bus is now mounted for exactly the lifetime of an in-room
  session, regardless of which leaf widget renders.
- src/hooks/rooms/widgets/usePollWidget.ts (compat shim) is reduced
  to a one-liner that just returns usePollActions(). It is still
  deprecated; remove once nothing imports it.

Verification
- yarn eslint on the two touched files: 1 pre-existing error
  (the same FC<{}> in RoomWidgetsView that was there before — baseline
  unchanged; I deliberately did not touch it in this commit to keep
  the diff minimal).
- yarn test: 22/22 still passing.
- grep confirms usePollWidget has zero in-tree consumers; the only
  importer is the barrel re-export.

src/components/room/widgets/RoomWidgetsView.tsx

@@ -2,7 +2,7 @@ import { GetRoomEngine, RoomEngineObjectEvent, RoomEngineRoomAdEvent, RoomEngine
 import { FC } from 'react';
 import { DispatchUiEvent, LocalizeText, NotificationAlertType, RoomWidgetUpdateRoomObjectEvent } from '../../../api';
 import { WidgetErrorBoundary } from '../../../common';
-import { useNitroEvent, useNotification, useRoom } from '../../../hooks';
+import { useNitroEvent, useNotification, usePollSubscriptions, useRoom } from '../../../hooks';
 import { AvatarInfoWidgetView } from './avatar-info/AvatarInfoWidgetView';
 import { ChatInputView } from './chat-input/ChatInputView';
 import { ChatWidgetView } from './chat/ChatWidgetView';
@@ -22,6 +22,11 @@ export const RoomWidgetsView: FC<{}> = props =>
     const { roomSession = null } = useRoom();
     const { simpleAlert = null } = useNotification();
 
+    // Bridge RoomSessionPollEvent (OFFER/ERROR/CONTENT) onto the UI bus
+    // for the lifetime of the room session. Single mount point so the
+    // listeners are not re-registered per widget render.
+    usePollSubscriptions();
+
     useNitroEvent<RoomZoomEvent>(RoomZoomEvent.ROOM_ZOOM, event => GetRoomEngine().setRoomInstanceRenderingCanvasScale(event.roomId, 1, (((event.level)<1) ? 0.5 : (1 << (Math.floor(event.level) - 1))), null, null, event.isFlipForced));
 
     useNitroEvent<RoomEngineObjectEvent>(