fix(usage): clarify spend summary window

Generated-By: PostHog Code
Task-Id: 35976f6d-329c-4b2e-9e38-cdeec8968ea1

Author: tatoalo

packages/ui/src/features/usage/components/SpendKpiStrip.tsx

@@ -1,5 +1,6 @@
 import {
   formatUsd,
+  formatWindow,
   type SpendAnalysisFilledDay,
   windowDays,
 } from "@posthog/core/billing/spendAnalysisFormat";
@@ -41,6 +42,7 @@ export function SpendKpiStrip({ data, filledDays }: SpendKpiStripProps) {
   const costSeries = filledDays?.map((d) => Math.max(0, d.cost_usd));
   const eventSeries = filledDays?.map((d) => d.event_count);
   const latestDay = filledDays?.at(-1);
+  const windowLabel = formatWindow(summary.date_from, summary.date_to);
 
   return (
     <Flex className="overflow-hidden rounded-(--radius-3) border border-(--gray-5) bg-(--color-panel-solid)">
@@ -64,6 +66,7 @@ export function SpendKpiStrip({ data, filledDays }: SpendKpiStripProps) {
           formatValue={formatUsd}
           change={null}
           subtitle={costSeries ? undefined : `${codeShare}% of total`}
+          restingSubtitle={windowLabel}
           sparklineHeight={28}
         />
       </KpiCell>
@@ -76,6 +79,7 @@ export function SpendKpiStrip({ data, filledDays }: SpendKpiStripProps) {
           theme={theme}
           formatValue={(v) => v.toLocaleString()}
           change={null}
+          restingSubtitle={windowLabel}
           sparklineHeight={28}
         />
       </KpiCell>