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。

frontend/app/(main)/nodes/components/disk-io-trend-chart.tsx

@@ -9,16 +9,25 @@ import {
   CardTitle,
 } from '@/components/ui/card';
 import type { DiskIOTrendPoint } from '@/lib/services/openflare';
+import { formatBytesPerSecond } from '@/lib/utils/metrics';
 
-import {
-  formatBytes,
-  formatTrendHour,
-} from '../../components/dashboard/dashboard-utils';
+import { formatTrendHour } from '../../components/dashboard/dashboard-utils';
+
+/** Backend disk points are per-hour totals; chart displays bytes/s within each hour. */
+const DISK_BUCKET_SECONDS = 3600;
+
+function diskBytesToRate(bytes: number) {
+  return bytes > 0 ? bytes / DISK_BUCKET_SECONDS : 0;
+}
+
+function formatDiskRate(bytesPerSecond: number) {
+  return formatBytesPerSecond(bytesPerSecond, 1, { zeroText: '0 B' });
+}
 
 export function DiskIOTrendChart({
   points,
   title = '24 小时磁盘 IO 趋势',
-  description = '观察磁盘读写变化，辅助判断日志放大、缓存抖动或磁盘压力。',
+  description = '按小时展示磁盘读写速率（B/s），辅助判断日志放大、缓存抖动或磁盘压力。',
 }: {
   points: DiskIOTrendPoint[];
   title?: string;
@@ -35,23 +44,27 @@ export function DiskIOTrendChart({
           labels={points.map((point) =>
             formatTrendHour(point.bucket_started_at),
           )}
-          summaryScope='total'
-          summaryHint='近 24 小时'
-          yAxisValueFormatter={formatBytes}
+          summaryScope='average'
+          summaryHint='近 24 小时 · 平均速率'
+          yAxisValueFormatter={formatDiskRate}
           series={[
             {
               label: '磁盘读',
               color: '#a78bfa',
               fillColor: 'rgba(167, 139, 250, 0.14)',
               variant: 'area',
-              values: points.map((point) => point.disk_read_bytes),
-              valueFormatter: formatBytes,
+              values: points.map((point) =>
+                diskBytesToRate(point.disk_read_bytes),
+              ),
+              valueFormatter: formatDiskRate,
             },
             {
               label: '磁盘写',
               color: '#fb7185',
-              values: points.map((point) => point.disk_write_bytes),
-              valueFormatter: formatBytes,
+              values: points.map((point) =>
+                diskBytesToRate(point.disk_write_bytes),
+              ),
+              valueFormatter: formatDiskRate,
             },
           ]}
         />