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_latency_histogram_buckets.go

@@ -0,0 +1,64 @@
+package repository
+
+import (
+	"fmt"
+	"strings"
+)
+
+type latencyHistogramBucket struct {
+	upperMs int
+	label   string
+}
+
+var latencyHistogramBuckets = []latencyHistogramBucket{
+	{upperMs: 100, label: "0-100ms"},
+	{upperMs: 200, label: "100-200ms"},
+	{upperMs: 500, label: "200-500ms"},
+	{upperMs: 1000, label: "500-1000ms"},
+	{upperMs: 2000, label: "1000-2000ms"},
+	{upperMs: 0, label: "2000ms+"}, // default bucket
+}
+
+var latencyHistogramOrderedRanges = func() []string {
+	out := make([]string, 0, len(latencyHistogramBuckets))
+	for _, b := range latencyHistogramBuckets {
+		out = append(out, b.label)
+	}
+	return out
+}()
+
+func latencyHistogramRangeCaseExpr(column string) string {
+	var sb strings.Builder
+	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))
+	}
+
+	// Default bucket.
+	last := latencyHistogramBuckets[len(latencyHistogramBuckets)-1]
+	sb.WriteString(fmt.Sprintf("\tELSE '%s'\n", last.label))
+	sb.WriteString("END")
+	return sb.String()
+}
+
+func latencyHistogramRangeOrderCaseExpr(column string) string {
+	var sb strings.Builder
+	sb.WriteString("CASE\n")
+
+	order := 1
+	for _, b := range latencyHistogramBuckets {
+		if b.upperMs <= 0 {
+			continue
+		}
+		sb.WriteString(fmt.Sprintf("\tWHEN %s < %d THEN %d\n", column, b.upperMs, order))
+		order++
+	}
+
+	sb.WriteString(fmt.Sprintf("\tELSE %d\n", order))
+	sb.WriteString("END")
+	return sb.String()
+}