[web] Remove SubscriptionFormatters, format subscription dates in the frontend (#36409)

* [web] Remove SubscriptionFormatters, format subscription dates in the frontend

Replace the server-formatted nextPaymentDueAt/nextPaymentDueDate/
trialEndsAtFormatted fields with the raw periodEnd date and format in
the React dashboard (same strings as before, English + UTC). Also
consolidate hand-rolled trial checks onto isInFreeTrial /
SubscriptionHelper.isInTrial.

* [web] Remove the now-unused dateformat dependency

* [web] Address review: payment-dates unit test, UTC dates in acceptance test

Add a dedicated unit test asserting the exact formatted strings from
formatPaymentDate/formatPaymentDateTime, and use explicit UTC timestamps
in the SubscriptionDashboard acceptance fixtures instead of
local-timezone Date constructors.

GitOrigin-RevId: 16ac4f1098b14ef9f1478d22cf39c1357ead7dea

services/web/frontend/js/features/subscription/context/subscription-dashboard-context.tsx

@@ -33,6 +33,7 @@ import { formatCurrency } from '@/shared/utils/currency'
 import { ManagedInstitution } from '../../../../../types/subscription/dashboard/managed-institution'
 import { Publisher } from '../../../../../types/subscription/dashboard/publisher'
 import { formatTime } from '@/features/utils/format-date'
+import { formatPaymentDateTime } from '../util/payment-dates'
 
 type SubscriptionDashboardContextValue = {
   groupPlanToChangeToCode: string
@@ -150,7 +151,7 @@ export function SubscriptionDashboardProvider({
       !personalSubscription.payment.pausedAt ||
       !personalSubscription.payment.remainingPauseCycles
     ) {
-      return personalSubscription.payment.nextPaymentDueAt
+      return formatPaymentDateTime(personalSubscription.payment.periodEnd)!
     }
     const pausedDate = new Date(personalSubscription.payment.pausedAt)
     pausedDate.setMonth(