feat: add 24-hour traffic and capacity trend charts to dashboard and node detail pages

- Implemented TrendChart component for visualizing traffic and capacity trends.
- Enhanced DashboardOverview and NodeDetailPage components to display 24-hour request and capacity trends.
- Updated types to include traffic and capacity trend data structures.
- Created observability trends service to aggregate traffic and capacity data.
- Added tests for traffic report generation and trend data handling.
- Introduced new dependencies for charting (echarts and echarts-for-react).

atsf_server/model/node_metric_snapshot.go

@@ -37,3 +37,12 @@ func ListNodeMetricSnapshots(nodeID string, since time.Time, limit int) (snapsho
 	err = query.Find(&snapshots).Error
 	return snapshots, err
 }
+
+func ListMetricSnapshotsSince(since time.Time) (snapshots []*NodeMetricSnapshot, err error) {
+	query := DB.Order("captured_at desc")
+	if !since.IsZero() {
+		query = query.Where("captured_at >= ?", since)
+	}
+	err = query.Find(&snapshots).Error
+	return snapshots, err
+}