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/stt-handlers.ts

@@ -29,8 +29,9 @@ export function registerSTTHandlers(): void {
     try {
       const stt = getLocalSTTService()
       return ipcSuccess(stt.getStatus())
-    } catch {
-      return ipcError(ErrorCode.STTSidecarCommunicationFailed, 'Failed to get STT status')
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error)
+      return ipcError(ErrorCode.STTSidecarCommunicationFailed, `Failed to get STT status: ${message}`)
     }
   })
 
@@ -38,8 +39,9 @@ export function registerSTTHandlers(): void {
     try {
       const stt = getLocalSTTService()
       return ipcSuccess(await stt.getModels())
-    } catch {
-      return ipcError(ErrorCode.STTModelNotFound, 'Failed to get models')
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error)
+      return ipcError(ErrorCode.STTModelNotFound, `Failed to get models: ${message}`)
     }
   })
 
@@ -53,8 +55,9 @@ export function registerSTTHandlers(): void {
       const stt = getLocalSTTService()
       await stt.initialize(params.modelId)
       return ipcSuccess(undefined)
-    } catch {
-      return ipcError(ErrorCode.STTModelLoadFailed, 'Failed to set STT model')
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error)
+      return ipcError(ErrorCode.STTModelLoadFailed, `Failed to set STT model: ${message}`)
     }
   })