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/components/media/MediaControls.tsx

@@ -11,7 +11,7 @@ export const MediaControl = as<'div', MediaControlProps>(
   ({ before, after, leftControl, rightControl, children, ...props }, ref) => (
     <Box grow="Yes" direction="Column" gap="300" {...props} ref={ref}>
       {before && <Box direction="Column">{before}</Box>}
-      <Box alignItems="Center" gap="200">
+      <Box alignItems="Center" gap="200" wrap="Wrap">
         <Box alignItems="Center" grow="Yes" gap="Inherit">
           {leftControl}
         </Box>