feat(usage): add resource-usage API client, meta hook, and shared utils

The data layer the resource tabs build on:
- apis/resource.ts: adapter over the unified metered_usage read API
  (resource/gpu-instances/storage/summary/events breakdowns), flattening
  the server's generic shape into the per-tab item shape.
- hooks/use-resource-meta.ts: loads creators/instances/volumes filter
  options for the current scope.
- utils/time-buckets.ts: day/week/month/hour bucket keys + range fill.
- utils/export-breakdown.ts: derive Excel columns from antd table specs.

src/pages/usage/utils/export-breakdown.ts

@@ -0,0 +1,50 @@
+/**
+ * Export a resource-breakdown table to Excel — the GPU Instances / Storage
+ * tabs' counterpart to the Tokens tab export.
+ *
+ * Columns are derived from the same antd column specs the table renders, so the
+ * export always matches what's on screen (whichever group_by tab is active).
+ * Raw values are written (not the table's formatted render output) so numbers
+ * stay sortable / calculable in the spreadsheet.
+ */
+import { exportJsonToExcel } from '@gpustack/core-ui/excel';
+
+export interface ExportColumn {
+  title: string;
+  dataIndex: string;
+}
+
+// Keep only real data columns (drop index / render-only columns), and only
+// those whose title is a plain string so the header is meaningful.
+export const toExportColumns = (columns: any[]): ExportColumn[] =>
+  (columns || [])
+    .filter(
+      (c) => typeof c?.dataIndex === 'string' && typeof c?.title === 'string'
+    )
+    .map((c) => ({
+      title: c.title as string,
+      dataIndex: c.dataIndex as string
+    }));
+
+export const exportBreakdownRows = (
+  rows: any[],
+  columns: ExportColumn[],
+  fileName: string,
+  sheetName = 'usage'
+): void => {
+  const fields = columns.map((c) => c.dataIndex);
+  const fieldLabels = Object.fromEntries(
+    columns.map((c) => [c.dataIndex, c.title])
+  );
+  const jsonData = (rows || []).map((r) => {
+    const o: Record<string, any> = {};
+    columns.forEach((c) => {
+      o[c.dataIndex] = r?.[c.dataIndex] ?? '';
+    });
+    return o;
+  });
+  exportJsonToExcel({
+    fileName,
+    sheets: [{ jsonData, sheetName, fields, fieldLabels, formatMap: {} }]
+  });
+};