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/llm-handlers.ts

@@ -60,8 +60,9 @@ export function registerLLMHandlers(): void {
     try {
       const models = await getLocalLLMService().getModels()
       return ipcSuccess(models)
-    } catch {
-      return ipcError(ErrorCode.LLMServerUnreachable, 'Failed to get models')
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error)
+      return ipcError(ErrorCode.LLMServerUnreachable, `Failed to get models: ${message}`)
     }
   })
 
@@ -91,8 +92,9 @@ export function registerLLMHandlers(): void {
         processingTimeMs: Math.round(performance.now() - start),
         tokenCount: 0
       })
-    } catch {
-      return ipcError(ErrorCode.LLMProcessingFailed, 'LLM processing failed')
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error)
+      return ipcError(ErrorCode.LLMProcessingFailed, `LLM processing failed: ${message}`)
     }
   })