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/main/ipc/cloud-sync-handlers.ts

@@ -0,0 +1,121 @@
+// src/main/ipc/cloud-sync-handlers.ts
+// Phase V2-4: CloudSync IPC 핸들러
+
+import { ipcMain, BrowserWindow } from 'electron'
+import { IPC_CHANNELS } from '@d3ro/core/ipc-channels'
+import { D3ROError, ErrorCode } from '@d3ro/core/errors'
+import type { IPCResult } from '@d3ro/core/errors'
+import { getCloudSyncService } from '../services/CloudSyncService'
+import { configSet } from '../services/ConfigService'
+import { getLogger } from '../services/LoggerService'
+
+const logger = getLogger('cloud-sync-handlers')
+
+interface SignInParams {
+  provider: 'google' | 'github'
+}
+
+interface ConfigureParams {
+  url: string
+  anonKey: string
+}
+
+function ok<T>(data: T): IPCResult<T> {
+  return { success: true, data }
+}
+
+function fail(error: unknown): IPCResult<never> {
+  if (error instanceof D3ROError) {
+    return { success: false, error: { code: error.code, message: error.message } }
+  }
+  const message = error instanceof Error ? error.message : String(error)
+  return {
+    success: false,
+    error: { code: ErrorCode.LLMProcessingFailed, message }
+  }
+}
+
+export function registerCloudSyncHandlers(): void {
+  const sync = getCloudSyncService()
+
+  ipcMain.handle(IPC_CHANNELS.CLOUD_SYNC.GET_STATE, () => {
+    try {
+      return ok(sync.getState())
+    } catch (e) {
+      return fail(e)
+    }
+  })
+
+  ipcMain.handle(IPC_CHANNELS.CLOUD_SYNC.CONFIGURE, async (_e, params: ConfigureParams) => {
+    try {
+      configSet('supabaseUrl' as never, params.url as never)
+      configSet('supabaseAnonKey' as never, params.anonKey as never)
+      // CloudSyncService 재초기화
+      await sync.init()
+      return ok(sync.getState())
+    } catch (e) {
+      return fail(e)
+    }
+  })
+
+  ipcMain.handle(IPC_CHANNELS.CLOUD_SYNC.SIGN_IN, async (_e, params: SignInParams) => {
+    try {
+      await sync.startSignIn(params.provider)
+      return ok({ started: true })
+    } catch (e) {
+      return fail(e)
+    }
+  })
+
+  ipcMain.handle(IPC_CHANNELS.CLOUD_SYNC.HANDLE_CALLBACK, async (_e, params: { code: string }) => {
+    try {
+      await sync.handleAuthCallback(params.code)
+      return ok(sync.getState())
+    } catch (e) {
+      return fail(e)
+    }
+  })
+
+  ipcMain.handle(IPC_CHANNELS.CLOUD_SYNC.SIGN_OUT, async () => {
+    try {
+      await sync.signOut()
+      return ok(sync.getState())
+    } catch (e) {
+      return fail(e)
+    }
+  })
+
+  ipcMain.handle(IPC_CHANNELS.CLOUD_SYNC.PUSH_ALL, async () => {
+    try {
+      const result = await sync.pushAll()
+      configSet('cloudSyncLastAt' as never, Date.now() as never)
+      return ok(result)
+    } catch (e) {
+      return fail(e)
+    }
+  })
+
+  // 이벤트 → renderer 브로드캐스트
+  function broadcast(channel: string, payload: unknown): void {
+    BrowserWindow.getAllWindows().forEach((win) => {
+      if (!win.isDestroyed()) {
+        win.webContents.send(channel, payload)
+      }
+    })
+  }
+
+  sync.on('auth-changed', (payload) => {
+    broadcast(IPC_CHANNELS.CLOUD_SYNC.AUTH_CHANGED, payload)
+  })
+  sync.on('sync-progress', (payload) => {
+    broadcast(IPC_CHANNELS.CLOUD_SYNC.SYNC_PROGRESS, payload)
+  })
+  sync.on('sync-complete', (payload) => {
+    broadcast(IPC_CHANNELS.CLOUD_SYNC.SYNC_COMPLETE, payload)
+  })
+  sync.on('sync-error', (payload) => {
+    broadcast(IPC_CHANNELS.CLOUD_SYNC.SYNC_ERROR, payload)
+  })
+
+  logger.info('Cloud Sync IPC handlers registered')
+}