fix(release): restore automatic updates by shipping the speech engine on demand

Auto-update could not work at all: the installer was 189 MB because it carried
the local speech engine and ffmpeg, and the download feed rejects uploads over
about 100 MiB, so update metadata could never be published.

The installer now leaves those components out and the app fetches them the first
time they are needed, verifying every part and the joined archive before
installing. The installer is 90.6 MiB, the update feed is published again, and
updates stay small because the engine is not re-sent on every release.

The fetch is visible and recoverable: the download runs with progress, a failed
install cleans up after itself, and Settings > STT shows the runtime status with
a manual download action for when the automatic one cannot run.

apps/desktop/src/main/services/FileTranscriptionService.ts

@@ -11,6 +11,7 @@ import { getSTTManager } from './stt/STTManager'
 import { getHistoryService } from './HistoryService'
 import { configGet } from './ConfigService'
 import { getFfmpegPath } from '../utils/paths'
+import { getRuntimeProvisioner } from './RuntimeProvisioner'
 import { getMainWindow } from '../windows/WindowManager'
 import { IPC_CHANNELS } from '@d3ro/core/ipc-channels'
 import { D3ROError, ErrorCode } from '@d3ro/core/errors'
@@ -250,6 +251,18 @@ class FileTranscriptionService extends EventEmitter {
     }
   }
 
+  /**
+   * ffmpeg 실행 파일을 확보한다. 설치본에는 ffmpeg을 넣지 않으므로
+   * 없으면 feed에서 내려받는다(파일 전사/회의 모드에서만 필요).
+   */
+  private async _ensureFfmpeg(): Promise<string> {
+    const resolved = getFfmpegPath()
+    if (resolved !== 'ffmpeg') return resolved
+
+    logger.info('ffmpeg이 없습니다 — 자동 다운로드를 시작합니다')
+    return getRuntimeProvisioner().ensure('ffmpeg')
+  }
+
   /**
    * ffmpeg로 미디어 파일을 PCM16 16kHz mono WAV로 변환
    */