feat(repository): 实现运维监控数据访问层

- 新增 ops 主仓库（ops_repo.go）
- 实现告警数据访问（ops_repo_alerts.go）
- 实现仪表板数据访问（ops_repo_dashboard.go）
- 实现直方图数据访问（ops_repo_histograms.go）
- 实现延迟直方图桶逻辑（ops_repo_latency_histogram_buckets.go）
- 新增延迟直方图桶测试（ops_repo_latency_histogram_buckets_test.go）
- 实现指标数据访问（ops_repo_metrics.go）
- 实现预聚合数据访问（ops_repo_preagg.go）
- 实现请求详情数据访问（ops_repo_request_details.go）
- 实现趋势数据访问（ops_repo_trends.go）
- 实现窗口统计数据访问（ops_repo_window_stats.go）
- 更新并发缓存支持 ops 场景
- 注册 repository 依赖注入

backend/internal/repository/ops_repo_histograms.go

@@ -0,0 +1,79 @@
+package repository
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/Wei-Shaw/sub2api/internal/service"
+)
+
+func (r *opsRepository) GetLatencyHistogram(ctx context.Context, filter *service.OpsDashboardFilter) (*service.OpsLatencyHistogramResponse, error) {
+	if r == nil || r.db == nil {
+		return nil, fmt.Errorf("nil ops repository")
+	}
+	if filter == nil {
+		return nil, fmt.Errorf("nil filter")
+	}
+	if filter.StartTime.IsZero() || filter.EndTime.IsZero() {
+		return nil, fmt.Errorf("start_time/end_time required")
+	}
+
+	start := filter.StartTime.UTC()
+	end := filter.EndTime.UTC()
+
+	join, where, args, _ := buildUsageWhere(filter, start, end, 1)
+	rangeExpr := latencyHistogramRangeCaseExpr("ul.duration_ms")
+	orderExpr := latencyHistogramRangeOrderCaseExpr("ul.duration_ms")
+
+	q := `
+SELECT
+  ` + rangeExpr + ` AS range,
+  COALESCE(COUNT(*), 0) AS count,
+  ` + orderExpr + ` AS ord
+FROM usage_logs ul
+` + join + `
+` + where + `
+AND ul.duration_ms IS NOT NULL
+GROUP BY 1, 3
+ORDER BY 3 ASC`
+
+	rows, err := r.db.QueryContext(ctx, q, args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	counts := make(map[string]int64, len(latencyHistogramOrderedRanges))
+	var total int64
+	for rows.Next() {
+		var label string
+		var count int64
+		var _ord int
+		if err := rows.Scan(&label, &count, &_ord); err != nil {
+			return nil, err
+		}
+		counts[label] = count
+		total += count
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+
+	buckets := make([]*service.OpsLatencyHistogramBucket, 0, len(latencyHistogramOrderedRanges))
+	for _, label := range latencyHistogramOrderedRanges {
+		buckets = append(buckets, &service.OpsLatencyHistogramBucket{
+			Range: label,
+			Count: counts[label],
+		})
+	}
+
+	return &service.OpsLatencyHistogramResponse{
+		StartTime:     start,
+		EndTime:       end,
+		Platform:      strings.TrimSpace(filter.Platform),
+		GroupID:       filter.GroupID,
+		TotalRequests: total,
+		Buckets:       buckets,
+	}, nil
+}