fix(desktop): macOS 단축키 표기 (Win/Ctrl/Alt → ⌘/⌃/⌥/⇧)

기존: HotkeyRecordModal에서 키 녹화 시 'Win+Shift+1' 같은 정적 displayLabel 저장
- KEY_DISPLAY_MAP이 Windows 전용 (91/92 → 'Win')
- SettingsModal HotkeyDisplay가 binding.displayLabel.split(' + ')로 chip 분리
  - 그런데 displayLabel은 join('+') (space 없음) — split이 작동 안 해서 단일 chip 'Win+Shift+1'
- macOS에서도 'Win'으로 표시되어 사용자 혼동

수정:
- preload/index.ts: process.platform 노출 (electronAPI.platform)
- renderer/utils/format-hotkey.ts 신규
  - formatHotkeySegments(binding) → 플랫폼별 segment 배열
    - macOS: ['⌘', '⇧', '1'] (⌃ ⌥ ⇧ ⌘ 순, Apple HIG)
    - Win/Linux: ['Ctrl', 'Win', 'Alt', 'Shift', '1']
  - formatHotkeyLabel(binding) → 단일 문자열
    - macOS: '⌘⇧1' (구분자 없음, Apple 표준)
    - Win/Linux: 'Ctrl + Shift + 1'
- 사용 위치 일괄 교체 (binding.displayLabel → format 헬퍼):
  - SettingsModal HotkeyDisplay (chip 표시)
  - SettingsModal Agent 모드 설명 ({{key}} 치환)
  - OnboardingModal 단축키 chip + 완료 화면
  - DashboardPage CrtDisplay 'PRESS X TO RECORD'
  - HotkeyRecordModal currentBinding 표시

displayLabel 필드는 ConfigService 호환을 위해 유지 (저장된 값은 그대로)

apps/desktop/src/renderer/components/OnboardingModal.tsx

@@ -18,6 +18,7 @@ import OpenInNewIcon from '@mui/icons-material/OpenInNew'
 import { d3roPalette, d3roFontMono, d3roShadow } from '@d3ro/ui/theme'
 import { Led } from '@d3ro/ui/components/ds'
 import { HotkeyRecordModal } from './HotkeyRecordModal'
+import { formatHotkeyLabel, formatHotkeySegments } from '../utils/format-hotkey'
 import { useI18n } from '@d3ro/i18n'
 import type { HotkeyBinding, AudioDevice } from '@d3ro/core/types'
 
@@ -167,9 +168,9 @@ export function OnboardingModal({ open, onClose }: OnboardingModalProps): React.
                 {hotkeyBinding ? (
                   <Stack direction="row" spacing={1} justifyContent="center" alignItems="center">
                     <Led color="green" size={8} />
-                    {hotkeyBinding.displayLabel.split(' + ').map((key) => (
+                    {formatHotkeySegments(hotkeyBinding).map((key, idx) => (
                       <Chip
-                        key={key}
+                        key={`${key}-${idx}`}
                         label={key}
                         sx={{
                           fontFamily: d3roFontMono,
@@ -247,7 +248,7 @@ export function OnboardingModal({ open, onClose }: OnboardingModalProps): React.
               </Typography>
               <Typography variant="body2" sx={{ color: d3roPalette.text.secondary, mb: 4 }}>
                 {hotkeyBinding
-                  ? t('onboarding.done.descWithKey', { key: hotkeyBinding.displayLabel })
+                  ? t('onboarding.done.descWithKey', { key: formatHotkeyLabel(hotkeyBinding) })
                   : t('onboarding.done.descNoKey')}
               </Typography>
               <Button variant="contained" onClick={handleFinish} fullWidth>