fix(mobile): deep-audit structural fixes — dialogs, toasts, call bar (N1)

From the 6-agent deep per-feature audit. Mobile-gated / consistency fixes;
desktop unchanged except two intentional dialog-width normalizations noted below.

- In-call control bar: wrap="Wrap" on the SequenceCard so the compact two-group
  row wraps on the narrowest phones (<=390px) instead of pushing End off-screen
  (M1 fixed the 500-750px band; this covers narrower). Desktop stays one row.
- In-call soundboard popout: clamp maxWidth to the viewport (like M5's screenshare
  popover) so it can't overflow a narrow phone.
- Report-Message dialog + "Seen by" (EventReaders) modals (Message.tsx x2 +
  RoomViewFollowing): add useModalStyle so they go full-screen on mobile like
  their sibling report/receipt modals (they floated as fixed cards before).
- In-app toast container: full-width toasts inset from both edges on mobile
  (ScreenSize.Mobile); a fixed 280-340px card previously overflowed a narrow
  phone. Desktop byte-identical (bottom-right floating card).
- Policy-list tabs + audio-controls rows: wrap="Wrap" (inert on desktop).

Intentional desktop deltas (normalizing to existing sibling modals, verified by
two review passes as consistent, not regressions): Report dialog max-width
380->480px; EventReaders modals 460->360px.

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

src/app/features/room/RoomViewFollowing.tsx

@@ -21,6 +21,7 @@ import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useRoomLatestRenderedEvent } from '../../hooks/useRoomLatestRenderedEvent';
 import { useRoomEventReaders } from '../../hooks/useRoomEventReaders';
 import { EventReaders } from '../../components/event-readers';
+import { useModalStyle } from '../../hooks/useModalStyle';
 import { stopPropagation } from '../../utils/keyboard';
 
 export function RoomViewFollowingPlaceholder() {
@@ -34,6 +35,7 @@ export const RoomViewFollowing = as<'div', RoomViewFollowingProps>(
   ({ className, room, ...props }, ref) => {
     const mx = useMatrixClient();
     const [open, setOpen] = useState(false);
+    const modalStyle = useModalStyle(360);
     const latestEvent = useRoomLatestRenderedEvent(room);
     const latestEventReaders = useRoomEventReaders(room, latestEvent?.getId());
     const names = latestEventReaders
@@ -55,7 +57,7 @@ export const RoomViewFollowing = as<'div', RoomViewFollowingProps>(
                   escapeDeactivates: stopPropagation,
                 }}
               >
-                <Modal variant="Surface" size="300">
+                <Modal variant="Surface" size="300" style={modalStyle}>
                   <EventReaders room={room} eventId={eventId} requestClose={() => setOpen(false)} />
                 </Modal>
               </FocusTrap>