feat(V2-4): 데스크톱 ↔ Supabase 동기화 (push only MVP)

CloudSyncService (싱글톤 + EventEmitter):
- Supabase 클라이언트 lazy init (configGet으로 url/key)
- safeStorage 기반 refresh token 영속화 (cloud-sync.token)
- startSignIn(provider): OAuth URL 발급 후 shell.openExternal로 외부 브라우저
- handleAuthCallback(code): code -> session 교환
- pushAll(): history/dictionary/meetings/meeting_memos/meeting_documents
  를 last_sync_at 이후 변경분만 upsert (onConflict: id)
- 이벤트: auth-changed / sync-progress / sync-complete / sync-error

Deep link (d3ro-voice://auth-callback):
- main/index.ts에 setAsDefaultProtocolClient
- macOS open-url 핸들러
- Windows second-instance argv 검사
- handleDeepLink로 URL 파싱 후 CloudSyncService로 전달

IPC:
- @d3ro/core/ipc-channels에 CLOUD_SYNC 채널 추가
- ipc/cloud-sync-handlers.ts (configure/signIn/signOut/pushAll/state)
- preload index.ts에 cloudSync 노출
- bootstrap의 cloud-sync 단계 추가

Renderer:
- CloudSyncSection 컴포넌트 신규
  - 미설정: Supabase URL/Key 입력 폼
  - 미로그인: Google/GitHub OAuth 버튼
  - 로그인: 사용자 이메일 + Sync Now + 진행 바 + 로그아웃
- d3roPalette/typoSx로 SSOT 준수, useI18n 사용

ConfigService 키 5종 추가:
- hfToken, diarizationEnabled (Phase 15.5 누락분 보충)
- supabaseUrl, supabaseAnonKey, cloudSyncLastAt (V2-4)
- packages/core types.ts AppConfig에도 동일하게 추가

검증:
- desktop typecheck OK
- desktop build OK
- 실제 Supabase 동기화는 사용자가 V2-2 배포 + 설정 입력 후 검증

apps/desktop/src/preload/index.ts

@@ -676,6 +676,37 @@ const electronAPI = {
     delete: (params: DeleteMeetingDocTemplateParams) =>
       invoke<void>(IPC_CHANNELS.MEETING_DOC_TEMPLATE.DELETE, params),
   },
+
+  cloudSync: {
+    getState: () =>
+      invoke<{
+        authenticated: boolean
+        userEmail: string | null
+        lastSyncAt: number | null
+        syncing: boolean
+      }>(IPC_CHANNELS.CLOUD_SYNC.GET_STATE),
+    configure: (params: { url: string; anonKey: string }) =>
+      invoke<unknown>(IPC_CHANNELS.CLOUD_SYNC.CONFIGURE, params),
+    signIn: (params: { provider: 'google' | 'github' }) =>
+      invoke<{ started: boolean }>(IPC_CHANNELS.CLOUD_SYNC.SIGN_IN, params),
+    signOut: () => invoke<unknown>(IPC_CHANNELS.CLOUD_SYNC.SIGN_OUT),
+    pushAll: () =>
+      invoke<{ pushed: number; errors: string[] }>(IPC_CHANNELS.CLOUD_SYNC.PUSH_ALL),
+    onAuthChanged: (callback: (data: { user: { id: string; email: string | null } | null }) => void) =>
+      on<{ user: { id: string; email: string | null } | null }>(
+        IPC_CHANNELS.CLOUD_SYNC.AUTH_CHANGED,
+        callback
+      ),
+    onSyncProgress: (callback: (data: { current: number; total: number; table: string }) => void) =>
+      on<{ current: number; total: number; table: string }>(
+        IPC_CHANNELS.CLOUD_SYNC.SYNC_PROGRESS,
+        callback
+      ),
+    onSyncComplete: (callback: (data: { pushed: number; errors: string[] }) => void) =>
+      on<{ pushed: number; errors: string[] }>(IPC_CHANNELS.CLOUD_SYNC.SYNC_COMPLETE, callback),
+    onSyncError: (callback: (data: { error: string }) => void) =>
+      on<{ error: string }>(IPC_CHANNELS.CLOUD_SYNC.SYNC_ERROR, callback),
+  },
 } as const
 
 contextBridge.exposeInMainWorld('electronAPI', electronAPI)