feat(api): add dashboard summary and system realtime endpoints

Add new admin API endpoints for dashboard metrics and system-wide
realtime statistics:

- Add /admin/dashboard/summary endpoint with aggregated metrics
  including requests, tokens, latency, masters, keys, and provider
  keys statistics with time period filtering
- Add /admin/realtime endpoint for system-level realtime stats
  aggregated across all masters
- Add status filter parameter to ListAPIKeys endpoint
- Add hour grouping option to log stats aggregation
- Update OpenAPI documentation with new endpoints and schemas

internal/api/realtime_handler.go

@@ -112,3 +112,73 @@ func (h *MasterHandler) GetSelfRealtime(c *gin.Context) {
 	}
 	c.JSON(http.StatusOK, toMasterRealtimeView(stats))
 }
+
+// SystemRealtimeView represents system-level realtime statistics
+type SystemRealtimeView struct {
+	QPS              int64                       `json:"qps"`
+	RPM              int64                       `json:"rpm"`
+	RateLimitedCount int64                       `json:"rate_limited_count"`
+	ByMaster         []MasterRealtimeSummaryView `json:"by_master"`
+	UpdatedAt        *int64                      `json:"updated_at,omitempty"`
+}
+
+// MasterRealtimeSummaryView is a brief summary of a master's realtime stats
+type MasterRealtimeSummaryView struct {
+	MasterID    uint  `json:"master_id"`
+	QPS         int64 `json:"qps"`
+	RateLimited bool  `json:"rate_limited"`
+}
+
+// GetAdminRealtime godoc
+// @Summary      System-level realtime stats (admin)
+// @Description  Return aggregated realtime counters across all masters
+// @Tags         admin
+// @Produce      json
+// @Security     AdminAuth
+// @Success      200  {object}  SystemRealtimeView
+// @Failure      500  {object}  gin.H
+// @Router       /admin/realtime [get]
+func (h *AdminHandler) GetAdminRealtime(c *gin.Context) {
+	if h.statsService == nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "stats service not configured"})
+		return
+	}
+
+	// Get all active master IDs
+	var masterIDs []uint
+	if err := h.db.Model(&model.Master{}).
+		Where("status = ?", "active").
+		Pluck("id", &masterIDs).Error; err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to load masters", "details": err.Error()})
+		return
+	}
+
+	stats, err := h.statsService.GetSystemRealtimeSnapshot(c.Request.Context(), masterIDs)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to load realtime stats", "details": err.Error()})
+		return
+	}
+
+	var updatedAt *int64
+	if stats.UpdatedAt != nil {
+		sec := stats.UpdatedAt.Unix()
+		updatedAt = &sec
+	}
+
+	byMaster := make([]MasterRealtimeSummaryView, 0, len(stats.ByMaster))
+	for _, m := range stats.ByMaster {
+		byMaster = append(byMaster, MasterRealtimeSummaryView{
+			MasterID:    m.MasterID,
+			QPS:         m.QPS,
+			RateLimited: m.RateLimited,
+		})
+	}
+
+	c.JSON(http.StatusOK, SystemRealtimeView{
+		QPS:              stats.TotalQPS,
+		RPM:              stats.TotalRPM,
+		RateLimitedCount: stats.RateLimitedCount,
+		ByMaster:         byMaster,
+		UpdatedAt:        updatedAt,
+	})
+}