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.go

@@ -172,7 +172,7 @@ LIMIT $` + itoa(len(args)+1) + ` OFFSET $` + itoa(len(args)+2)
 	if err != nil {
 		return nil, err
 	}
-	defer rows.Close()
+	defer func() { _ = rows.Close() }()
 
 	out := make([]*service.OpsErrorLog, 0, pageSize)
 	for rows.Next() {

backend/internal/repository/ops_repo_alerts.go

@@ -41,7 +41,7 @@ ORDER BY id DESC`
 	if err != nil {
 		return nil, err
 	}
-	defer rows.Close()
+	defer func() { _ = rows.Close() }()
 
 	out := []*service.OpsAlertRule{}
 	for rows.Next() {
@@ -361,7 +361,7 @@ LIMIT ` + limitArg
 	if err != nil {
 		return nil, err
 	}
-	defer rows.Close()
+	defer func() { _ = rows.Close() }()
 
 	out := []*service.OpsAlertEvent{}
 	for rows.Next() {

backend/internal/repository/ops_repo_dashboard.go

@@ -344,12 +344,12 @@ func (r *opsRepository) listHourlyMetricsRows(ctx context.Context, filter *servi
 		if platform != "" {
 			where += fmt.Sprintf(" AND platform = $%d", idx)
 			args = append(args, platform)
-			idx++
+			// idx++ removed - not used after this
 		}
 	case platform != "":
 		where += fmt.Sprintf(" AND platform = $%d AND group_id IS NULL", idx)
 		args = append(args, platform)
-		idx++
+		// idx++ removed - not used after this
 	default:
 		where += " AND platform IS NULL AND group_id IS NULL"
 	}

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()
 }