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/instruction-handlers.ts

@@ -24,8 +24,9 @@ export function registerInstructionHandlers(): void {
       try {
         const result = getCustomInstructionService().create(params)
         return ipcSuccess(result)
-      } catch {
-        return ipcError(ErrorCode.ConfigWriteFailed, 'Failed to create instruction')
+      } catch (error) {
+        const message = error instanceof Error ? error.message : String(error)
+        return ipcError(ErrorCode.ConfigWriteFailed, `Failed to create instruction: ${message}`)
       }
     }
   )
@@ -36,8 +37,9 @@ export function registerInstructionHandlers(): void {
       try {
         const result = getCustomInstructionService().update(params.id, params.data)
         return ipcSuccess(result)
-      } catch {
-        return ipcError(ErrorCode.ConfigWriteFailed, 'Failed to update instruction')
+      } catch (error) {
+        const message = error instanceof Error ? error.message : String(error)
+        return ipcError(ErrorCode.ConfigWriteFailed, `Failed to update instruction: ${message}`)
       }
     }
   )