fix(composer): collapse mobile action buttons behind a "+" overflow menu

On phones the composer's 7-8 secondary action buttons wrapped into a tall
multi-row stack ("massive height"). Mobile now shows a single compact row —
[ + | input | emoji | send ] — where "+" toggles a collapsible row (above the
formatting toolbar) holding attach, GIF, location, poll, voice, formatting and
schedule. Desktop is unchanged (isMobile === false; the mobile branches are
never entered and composerOverflow stays null).

The after-builder stashes the collapsed buttons in a render-local `let` that
the bottom slot reads; safe because JSX props evaluate in source order within
one render (verified by review). Emoji/Send stay inline; the emoji and GIF
PopOut anchors still resolve wherever their button renders.

Review fixes folded in: the "+" toggle uses aria-expanded + aria-controls
(dropped the redundant aria-pressed) pointing at the labelled role="group"
overflow row; the voice recorder's idle mic button gets the @media-gated
MobileTouchTarget 44px target so the overflow row is uniformly tappable.

Two review agents (correctness + UX/a11y); gate-green (tsc, eslint, prettier,
914 tests, build). Visual confirmation still wants a real device per
LOTUS_TESTING.

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

src/app/components/VoiceMessageRecorder.tsx

@@ -2,6 +2,7 @@ import React, { useCallback, useEffect, useRef, useState } from 'react';
 import { Box, Icon, IconButton, Icons, Text, color, config, toRem } from 'folds';
 import { useSetting } from '../state/hooks/settings';
 import { settingsAtom } from '../state/settings';
+import { MobileTouchTarget } from '../styles/mobile.css';
 
 type RecorderState = 'idle' | 'recording' | 'paused' | 'preview';
 
@@ -239,6 +240,7 @@ export function VoiceMessageRecorder({ onSend, onError }: VoiceRecorderProps) {
   if (state === 'idle') {
     return (
       <IconButton
+        className={MobileTouchTarget}
         onClick={startRecording}
         aria-label="Record voice message"
         variant="SurfaceVariant"