fix(site): set spend today range to end of day (#26992)

Selecting Today in the AI spend usage date range picker sent an end date
rounded to the next hour, which made refreshed usage pages show stale
partial-day data.

This lets the shared date range picker keep its existing next-hour
default for template insights while the spend usage and drill-in pickers
request an end-of-day boundary for Today.

Closes
https://linear.app/codercom/issue/CODAGT-751/date-range-picker-uses-end-of-hour-for-today

Generated by Coder Agents.

site/src/pages/AISettingsPage/SpendPage/SpendPage.tsx

@@ -21,6 +21,7 @@ import { useAuthenticated } from "#/hooks/useAuthenticated";
 import { usePaginatedQuery } from "#/hooks/usePaginatedQuery";
 import { RequirePermission } from "#/modules/permissions/RequirePermission";
 import { SpendPageView } from "./SpendPageView";
+import { toExclusiveEndOfDayDateRange } from "./utils/dateRange";
 
 const startDateSearchParam = "startDate";
 const endDateSearchParam = "endDate";
@@ -132,11 +133,13 @@ const SpendPage: FC<SpendPageProps> = ({ now }) => {
 	};
 
 	const onDateRangeChange = (value: DateRangeValue) => {
+		const nextDateRange = toExclusiveEndOfDayDateRange(value);
+
 		setSearchParams(
 			(prev) => {
 				const next = new URLSearchParams(prev);
-				next.set(startDateSearchParam, value.startDate.toISOString());
-				next.set(endDateSearchParam, value.endDate.toISOString());
+				next.set(startDateSearchParam, nextDateRange.startDate.toISOString());
+				next.set(endDateSearchParam, nextDateRange.endDate.toISOString());
 				next.delete("page");
 				return next;
 			},

site/src/pages/AISettingsPage/SpendPage/utils/dateRange.test.ts

@@ -1,5 +1,32 @@
 import { describe, expect, it } from "vitest";
-import { formatUsageDateRange, toInclusiveDateRange } from "./dateRange";
+import {
+	formatUsageDateRange,
+	toExclusiveEndOfDayDateRange,
+	toInclusiveDateRange,
+} from "./dateRange";
+
+describe("toExclusiveEndOfDayDateRange", () => {
+	it("moves a non-midnight end date to the next midnight", () => {
+		const startDate = new Date(2025, 5, 1, 0, 0, 0, 0);
+		const endDate = new Date(2025, 5, 8, 14, 30, 0, 0);
+		const result = toExclusiveEndOfDayDateRange({ startDate, endDate });
+		expect(result.endDate).toEqual(new Date(2025, 5, 9, 0, 0, 0, 0));
+	});
+
+	it("returns unchanged when the end date is already midnight", () => {
+		const startDate = new Date(2025, 5, 1, 0, 0, 0, 0);
+		const endDate = new Date(2025, 5, 8, 0, 0, 0, 0);
+		const result = toExclusiveEndOfDayDateRange({ startDate, endDate });
+		expect(result.endDate).toBe(endDate);
+	});
+
+	it("preserves startDate", () => {
+		const startDate = new Date(2025, 5, 1, 0, 0, 0, 0);
+		const endDate = new Date(2025, 5, 8, 14, 30, 0, 0);
+		const result = toExclusiveEndOfDayDateRange({ startDate, endDate });
+		expect(result.startDate).toBe(startDate);
+	});
+});
 
 describe("toInclusiveDateRange", () => {
 	it("subtracts 1ms when endDateIsExclusive is true and end date is midnight", () => {

site/src/pages/AISettingsPage/SpendPage/utils/dateRange.ts

@@ -16,6 +16,19 @@ function isMidnight(date: Date): boolean {
 	);
 }
 
+export function toExclusiveEndOfDayDateRange(
+	dateRange: DateRangeValue,
+): DateRangeValue {
+	if (isMidnight(dateRange.endDate)) {
+		return dateRange;
+	}
+
+	return {
+		startDate: dateRange.startDate,
+		endDate: dayjs(dateRange.endDate).startOf("day").add(1, "day").toDate(),
+	};
+}
+
 /**
  * When the user picks an explicit date range whose end boundary is
  * midnight of the following day, adjust it by −1 ms so the