Added a "Published in the last X days" filter, applied by the backend

GET /api/opportunities takes released_from, an RFC 3339 time, and lists
only the opportunities whose latest release is at or after it. It works
with paging and with changed_after, which keeps the same batch either
way; an invalid value is 400.

The frontend's filter defaults to 7 days, from midnight UK time, and
sends it with every load and catch-up, so a year of opportunities isn't
downloaded to show a week's. Changing the days loads the list again;
Clear filters goes back to 7.

web/src/lib/filterOpportunities.test.ts

@@ -7,6 +7,7 @@ import {
   emptyFilters,
   filterOpportunities,
   NOT_MARKED,
+  releasedFrom,
   statusLabel,
   statusOptions,
 } from './filterOpportunities';
@@ -73,6 +74,16 @@ test('activeFilterCount counts the filters in use', () => {
   expect(
     activeFilterCount({ ...emptyFilters(), title: ' ', smeSuitable: true, showHidden: true }),
   ).toBe(2);
+  expect(activeFilterCount({ ...emptyFilters(), releasedWithinDays: 30 })).toBe(1);
+});
+
+test('releasedFrom is the start of the day that many days ago, in UK time', () => {
+  // 19 October 2026 is in British Summer Time; 12 October's midnight is 23:00 UTC.
+  const now = new Date('2026-10-19T09:30:00Z');
+  expect(releasedFrom(7, now)).toBe('2026-10-11T23:00:00.000Z');
+  expect(releasedFrom(0, now)).toBe('2026-10-18T23:00:00.000Z');
+  // Across the end of BST (25 October), midnight is 00:00 UTC again.
+  expect(releasedFrom(7, new Date('2026-11-02T12:00:00Z'))).toBe('2026-10-26T00:00:00.000Z');
 });
 
 test('statusOptions lists the known statuses, then others sorted', () => {

web/src/lib/filterOpportunities.ts

@@ -3,12 +3,21 @@ import type { Opportunity, OpportunityStatus } from '@/types/Opportunities';
 import { OPPORTUNITY_STATUSES } from '@/types/Opportunities';
 import { parseDate } from './format';
 
+/** How many days back opportunities are loaded from, unless the user chooses otherwise. */
+export const DEFAULT_RELEASED_WITHIN_DAYS = 7;
+
 /** Marks filter option for opportunities with no marks at all. */
 export const NOT_MARKED = 'none';
 export type MarkFilter = OpportunityMark | typeof NOT_MARKED;
 
 /** What the table is filtered by. */
 export interface OpportunityFilters {
+  /**
+   * Only opportunities with a release in the last this many days, and
+   * today. The backend applies it (see releasedFrom); the rest are applied
+   * here.
+   */
+  releasedWithinDays: number;
   title: string;
   /** Empty means every status. */
   statuses: ReadonlySet<string>;
@@ -21,8 +30,12 @@ export interface OpportunityFilters {
   showHidden: boolean;
 }
 
-/** Filters that let every opportunity through, apart from hidden ones. */
+/**
+ * The filters to start with: the last DEFAULT_RELEASED_WITHIN_DAYS days'
+ * opportunities, apart from hidden ones.
+ */
 export const emptyFilters = (): OpportunityFilters => ({
+  releasedWithinDays: DEFAULT_RELEASED_WITHIN_DAYS,
   title: '',
   statuses: new Set(),
   marks: new Set(),
@@ -31,9 +44,13 @@ export const emptyFilters = (): OpportunityFilters => ({
   showHidden: false,
 });
 
-/** How many separate filters are in use, for the collapsed panel's badge. */
+/**
+ * How many separate filters are changed from emptyFilters, for the collapsed
+ * panel's badge.
+ */
 export const activeFilterCount = (filters: OpportunityFilters): number =>
   [
+    filters.releasedWithinDays !== DEFAULT_RELEASED_WITHIN_DAYS,
     filters.title.trim() !== '',
     filters.statuses.size > 0,
     filters.marks.size > 0,
@@ -46,6 +63,15 @@ export const activeFilterCount = (filters: OpportunityFilters): number =>
 export const hasActiveFilters = (filters: OpportunityFilters): boolean =>
   activeFilterCount(filters) > 0;
 
+/**
+ * The start of the day days before now, in local time, as an RFC 3339 time
+ * for the backend's released_from: 7 days on a Monday is from the Monday
+ * before, so a whole week and today.
+ */
+export function releasedFrom(days: number, now: Date = new Date()): string {
+  return new Date(now.getFullYear(), now.getMonth(), now.getDate() - days).toISOString();
+}
+
 /** The opportunities that pass filters, newest release first. */
 export function filterOpportunities(
   opportunities: readonly Opportunity[],