feat(ops): 添加 count_tokens 错误过滤功能

功能特性：
- 自动识别并标记 count_tokens 请求的错误
- 支持配置是否在统计中忽略 count_tokens 错误
- 错误数据完整保留，仅在统计时动态过滤

技术实现：
- ops_error_logger.go: 自动标记 count_tokens 请求
- ops_repo.go: INSERT 语句添加 is_count_tokens 字段
- ops_repo_dashboard.go: buildErrorWhere 核心过滤函数
- ops_repo_preagg.go: 预聚合统计中添加过滤
- ops_repo_trends.go: 趋势统计查询添加过滤（2 处）
- ops_settings_models.go: 添加 ignore_count_tokens_errors 配置
- ops_settings.go: 配置验证和默认值设置
- ops_port.go: 错误日志模型添加 IsCountTokens 字段

业务价值：
- count_tokens 是探测性请求，其错误不影响真实业务 SLA
- 用户可根据需求灵活控制是否计入统计
- 提升错误率、告警等运维指标的准确性

影响范围：
- Dashboard 概览统计
- 错误趋势图表
- 告警规则评估
- 预聚合指标（hourly/daily）
- 健康分数计算

backend/internal/repository/ops_repo.go

@@ -46,6 +46,7 @@ INSERT INTO ops_error_logs (
   severity,
   status_code,
   is_business_limited,
+  is_count_tokens,
   error_message,
   error_body,
   error_source,
@@ -64,7 +65,7 @@ INSERT INTO ops_error_logs (
   retry_count,
   created_at
 ) VALUES (
-  $1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13,$14,$15,$16,$17,$18,$19,$20,$21,$22,$23,$24,$25,$26,$27,$28,$29,$30,$31,$32,$33,$34
+  $1,$2,$3,$4,$5,$6,$7,$8,$9,$10,$11,$12,$13,$14,$15,$16,$17,$18,$19,$20,$21,$22,$23,$24,$25,$26,$27,$28,$29,$30,$31,$32,$33,$34,$35
 ) RETURNING id`
 
 	var id int64
@@ -88,6 +89,7 @@ INSERT INTO ops_error_logs (
 		opsNullString(input.Severity),
 		opsNullInt(input.StatusCode),
 		input.IsBusinessLimited,
+		input.IsCountTokens,
 		opsNullString(input.ErrorMessage),
 		opsNullString(input.ErrorBody),
 		opsNullString(input.ErrorSource),

backend/internal/repository/ops_repo_dashboard.go

@@ -964,8 +964,8 @@ func buildErrorWhere(filter *service.OpsDashboardFilter, start, end time.Time, s
 	}
 
 	idx := startIndex
-	clauses := make([]string, 0, 4)
-	args = make([]any, 0, 4)
+	clauses := make([]string, 0, 5)
+	args = make([]any, 0, 5)
 
 	args = append(args, start)
 	clauses = append(clauses, fmt.Sprintf("created_at >= $%d", idx))
@@ -974,6 +974,8 @@ func buildErrorWhere(filter *service.OpsDashboardFilter, start, end time.Time, s
 	clauses = append(clauses, fmt.Sprintf("created_at < $%d", idx))
 	idx++
 
+	clauses = append(clauses, "is_count_tokens = FALSE")
+
 	if groupID != nil && *groupID > 0 {
 		args = append(args, *groupID)
 		clauses = append(clauses, fmt.Sprintf("group_id = $%d", idx))

backend/internal/repository/ops_repo_preagg.go

@@ -78,7 +78,9 @@ error_base AS (
     status_code AS client_status_code,
     COALESCE(upstream_status_code, status_code, 0) AS effective_status_code
   FROM ops_error_logs
+  -- Exclude count_tokens requests from error metrics as they are informational probes
   WHERE created_at >= $1 AND created_at < $2
+    AND is_count_tokens = FALSE
 ),
 error_agg AS (
   SELECT

backend/internal/repository/ops_repo_trends.go

@@ -170,6 +170,7 @@ error_totals AS (
   FROM ops_error_logs
   WHERE created_at >= $1 AND created_at < $2
     AND COALESCE(status_code, 0) >= 400
+    AND is_count_tokens = FALSE  -- 排除 count_tokens 请求的错误
   GROUP BY 1
 ),
 combined AS (
@@ -243,6 +244,7 @@ error_totals AS (
     AND platform = $3
     AND group_id IS NOT NULL
     AND COALESCE(status_code, 0) >= 400
+    AND is_count_tokens = FALSE  -- 排除 count_tokens 请求的错误
   GROUP BY 1
 ),
 combined AS (