fix(lint): 修复 golangci-lint 检查问题

- 格式化代码（gofmt）
- 修复空指针检查（staticcheck）
- 删除未使用的函数（unused）

backend/internal/handler/ops_error_logger.go

@@ -1013,4 +1013,3 @@ func shouldSkipOpsErrorLog(ctx context.Context, ops *service.OpsService, message
 
 	return false
 }
-

backend/internal/repository/ops_repo.go

@@ -967,6 +967,7 @@ func buildOpsErrorLogsWhere(filter *service.OpsErrorLogFilter) (string, []any) {
 		args = append(args, phase)
 		clauses = append(clauses, "error_phase = $"+itoa(len(args)))
 	}
+	if filter != nil {
 		if owner := strings.TrimSpace(strings.ToLower(filter.Owner)); owner != "" {
 			args = append(args, owner)
 			clauses = append(clauses, "LOWER(COALESCE(error_owner,'')) = $"+itoa(len(args)))
@@ -975,6 +976,7 @@ func buildOpsErrorLogsWhere(filter *service.OpsErrorLogFilter) (string, []any) {
 			args = append(args, source)
 			clauses = append(clauses, "LOWER(COALESCE(error_source,'')) = $"+itoa(len(args)))
 		}
+	}
 	if resolvedFilter != nil {
 		args = append(args, *resolvedFilter)
 		clauses = append(clauses, "COALESCE(resolved,false) = $"+itoa(len(args)))

backend/internal/service/ops_service.go

@@ -612,11 +612,3 @@ func sanitizeErrorBodyForStorage(raw string, maxBytes int) (sanitized string, tr
 	return raw, false
 }
 
-func extractString(v any, key string) string {
-	root, ok := v.(map[string]any)
-	if !ok {
-		return ""
-	}
-	s, _ := root[key].(string)
-	return strings.TrimSpace(s)
-}