fix(i18n): backfill 120 missing keys + close 2 typo regressions from purchase refactor

Surface: users (and especially Серёжа в bugs topic) were seeing raw i18n keys
like `subscription.promoGroup.title` rendered as literal text on the renewal
screen. Audit found 118 keys referenced in code that were absent from all 4
locale files, plus 140 keys missing only in zh/fa (silently falling back to
Russian for those users).

Root causes:
- cf52999 (extract TariffPickerGrid) introduced `subscription.promoGroup.title`
  that never existed — should have been `subscription.promoGroup.yourGroup`.
- Subscription.tsx used `subscription.autopay.title` (object path) while
  SubscriptionListCard.tsx used `subscription.autopay` (leaf) — i18next can't
  hold both shapes for the same key.
- Many user-flow keys (subscription.notFound, subscriptions.empty, common.ok,
  successNotification.*, etc.) were never added when their components landed.
- Historical drift had ~140 keys in ru/en that never got zh/fa translations.

Fix:
- Rename TariffPickerGrid usage `promoGroup.title` → `promoGroup.yourGroup`.
- Rename Subscription.tsx usage `autopay.title` → `autopay`.
- Add 116 brand-new keys across ru/en/zh/fa (464 entries).
- Add 8 partially-missing keys (en+ru gaps) for landing periods, dashboard
  campaign/referrer stats, and promo offer failure counts.
- Translate 280 entries to close the zh/fa drift.

Final state: 0 keys missing in any of the 4 locale files for any code-referenced
translation key. Build + tsc green.

src/components/subscription/purchase/TariffPickerGrid.tsx

@@ -74,7 +74,7 @@ export function TariffPickerGrid({
           </div>
           <div>
             <div className="text-sm font-medium text-success-400">
-              {t('subscription.promoGroup.title', {
+              {t('subscription.promoGroup.yourGroup', {
                 name: tariffs.find((tariff) => tariff.promo_group_name)?.promo_group_name,
               })}
             </div>