[web] Update paywall copy for plans-2026 AI tiers (#33070)

* [web] Update paywall copy for plans-2026 AI tiers

Replace AI-related strings in upgrade/paywall UI when the
plans-2026-phase-1 flag is enabled:

- Add `higher_ai_allowance` ("Higher AI allowance") for paywall bullet
  lists and body text; keep `higher_ai_limits` ("Higher AI limits") for
  the subscriptions dashboard, which uses different wording per spec
- Update three locale strings to use "allowance" instead of "limits":
  `access_all_premium_features_ai`, `plus_additional_collaborators_and_more`,
  `upgrade_to_add_more_collaborators_and_more`
- Fix casing: `upgrade_to_review` "Upgrade to Review" → "Upgrade to review"
- Switch upgrade-benefits and onboarding prompt from `higher_ai_limits`
  to `higher_ai_allowance`
- Fix subscriptions free-plan to show `higher_ai_limits` instead of
  `get_unlimited_ai` under the plans2026 flag
- Fix compile-timeout button to show "Start free trial" under plans2026
  instead of "Start a free trial"
- Update two Cypress assertions for the new track-changes modal title

* Update extracted translations for higher AI allowance

* Remove "start a free trial" with exclamation

* Remove "get unlimited ai" translation entries

GitOrigin-RevId: 12300d94dc81c5407a21d4682d5714d7284c31b0

services/web/frontend/js/shared/components/upgrade-benefits.tsx

@@ -17,7 +17,7 @@ function UpgradeBenefits({ className }: { className?: string }) {
       <li>
         <Check />
         &nbsp;
-        {plans2026 ? t('unlimited_ai') : t('unlimited_projects')}
+        {plans2026 ? t('higher_ai_allowance') : t('unlimited_projects')}
       </li>
       <li>
         <Check />