feat(ops): 添加QPS脉搏线图并优化指标布局

- 添加实时QPS/TPS历史数据追踪（最近60个数据点）
- 在平均QPS/TPS上方添加SVG脉搏线图（sparkline）
- 将延迟和TTFT卡片的指标布局从2列改为3列
- 恢复Max指标显示（P95/P90/P50/Avg/Max）

backend/internal/service/ops_upstream_context.go

@@ -0,0 +1,31 @@
+package service
+
+import (
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+// Gin context keys used by Ops error logger for capturing upstream error details.
+// These keys are set by gateway services and consumed by handler/ops_error_logger.go.
+const (
+	OpsUpstreamStatusCodeKey   = "ops_upstream_status_code"
+	OpsUpstreamErrorMessageKey = "ops_upstream_error_message"
+	OpsUpstreamErrorDetailKey  = "ops_upstream_error_detail"
+)
+
+func setOpsUpstreamError(c *gin.Context, upstreamStatusCode int, upstreamMessage, upstreamDetail string) {
+	if c == nil {
+		return
+	}
+	if upstreamStatusCode > 0 {
+		c.Set(OpsUpstreamStatusCodeKey, upstreamStatusCode)
+	}
+	if msg := strings.TrimSpace(upstreamMessage); msg != "" {
+		c.Set(OpsUpstreamErrorMessageKey, msg)
+	}
+	if detail := strings.TrimSpace(upstreamDetail); detail != "" {
+		c.Set(OpsUpstreamErrorDetailKey, detail)
+	}
+}
+