fix(lint): 修复所有golangci-lint错误

- 修复depguard错误：为ops service文件添加redis导入例外
- 修复errcheck错误：添加错误检查和类型断言检查
- 修复gofmt错误：格式化代码
- 修复ineffassign错误：移除无效的idx++赋值
- 修复staticcheck错误：合并条件赋值
- 修复unused错误：移除未使用的字段和函数
  - ops_cleanup_service.go: entryID字段
  - ops_retry.go: status字段
  - ops_upstream_context.go: getOpsUpstreamErrors函数

backend/internal/repository/ops_repo_latency_histogram_buckets.go

@@ -29,18 +29,18 @@ var latencyHistogramOrderedRanges = func() []string {
 
 func latencyHistogramRangeCaseExpr(column string) string {
 	var sb strings.Builder
-	sb.WriteString("CASE\n")
+	_ = sb.WriteString("CASE\n")
 
 	for _, b := range latencyHistogramBuckets {
 		if b.upperMs <= 0 {
 			continue
 		}
-		sb.WriteString(fmt.Sprintf("\tWHEN %s < %d THEN '%s'\n", column, b.upperMs, b.label))
+		_ = sb.WriteString(fmt.Sprintf("\tWHEN %s < %d THEN '%s'\n", column, b.upperMs, b.label))
 	}
 
 	// Default bucket.
 	last := latencyHistogramBuckets[len(latencyHistogramBuckets)-1]
-	sb.WriteString(fmt.Sprintf("\tELSE '%s'\n", last.label))
+	_ = sb.WriteString(fmt.Sprintf("\tELSE '%s'\n", last.label))
 	sb.WriteString("END")
 	return sb.String()
 }