refactor(main): ipcSuccess/ipcError 헬퍼 통일 + catch(error) 패턴 (WS-PATTERN)

- cloud-sync-handlers 수동 ok/fail -> ipcSuccess/ipcError 헬퍼 (6 핸들러)
- catch {} -> catch(error) 에러 메시지 보강 32건 (11 ipc handler 파일)
KEEP: template-handlers(주석 명시 에러 무시), license-handlers(이미 헬퍼 사용),
       audio-handlers stop().catch(() => {})(의도적 무시)
정책: docs/REFACTOR_POLICY.md DP2

apps/desktop/src/main/ipc/voice-handlers.ts

@@ -34,8 +34,9 @@ export function registerVoiceHandlers(): void {
       await voice.startSession('dictation')
       const session = voice.currentSession
       return ipcSuccess({ sessionId: session?.id ?? params.sessionId ?? '' })
-    } catch {
-      return ipcError(ErrorCode.AudioCaptureStartFailed, 'Failed to start recording')
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error)
+      return ipcError(ErrorCode.AudioCaptureStartFailed, `Failed to start recording: ${message}`)
     }
   })
 
@@ -48,8 +49,9 @@ export function registerVoiceHandlers(): void {
         text: voice.currentSession?.transcription ?? '',
         durationMs: voice.currentSession ? Date.now() - voice.currentSession.startedAt : 0
       })
-    } catch {
-      return ipcError(ErrorCode.STTTranscriptionFailed, 'Failed to stop recording')
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error)
+      return ipcError(ErrorCode.STTTranscriptionFailed, `Failed to stop recording: ${message}`)
     }
   })