feat(obs): 去掉宿主机网卡趋势，磁盘读写改按速率展示

Agent 不再采集网卡累计字节，看板与节点网络图仅保留访问日志已提供/接收。
磁盘 IO 按小时换算为 B/s 曲线，摘要为近 24 小时平均速率，并同步 Swagger。

internal/apps/openflare/dashboard/logics.go

@@ -354,12 +354,9 @@ func compressCapacityTrendPoints(points []observability.CapacityTrendPoint) [][]
 func compressNetworkTrendPoints(points []observability.NetworkTrendPoint) [][]any {
 	rows := make([][]any, 0, len(points))
 	for _, point := range points {
-		// Compact layout (stable positions):
-		// [0] bucket, [1] host_rx, [2] host_tx, [3] bytes_received, [4] bytes_provided, [5] reported_nodes
+		// Compact layout: [0] bucket, [1] bytes_received, [2] bytes_provided, [3] reported_nodes
 		rows = append(rows, []any{
 			point.BucketStartedAt,
-			point.NetworkRxBytes,
-			point.NetworkTxBytes,
 			point.BytesReceived,
 			point.BytesProvided,
 			point.ReportedNodes,

internal/apps/openflare/dashboard/logics_test.go

@@ -149,7 +149,7 @@ func TestGetOverviewStructure(t *testing.T) {
 		require.Len(t, row, 4)
 	}
 	for _, row := range overview.Trends.Network24h {
-		require.Len(t, row, 6)
+		require.Len(t, row, 4)
 	}
 	for _, row := range overview.Trends.DiskIO24h {
 		require.Len(t, row, 4)