- New WebBackButton component: visible on web, hidden in Telegram
(native back button handles navigation there)
- Added to: Subscription detail, SubscriptionPurchase, RenewSubscription
- RenewSubscription: removed max-w-lg, grid layout for period cards
- RenewSubscription: display actual missing amount instead of {{missing}} placeholder
- SubscriptionPurchase: suppress "switch tariff" title in multi-tariff mode
(only renewal exists, no tariff switching)
Renewal flow (per-subscription):
- New /subscriptions/:id/renew page showing only period options for
the specific tariff with balance display and renew button
- PurchaseCTAButton links to /renew in multi-tariff mode
Purchase flow (new tariffs only):
- Hide already purchased tariffs (is_purchased flag from backend)
- Fallback UI when all tariffs are owned
- Types: added is_purchased, all_tariffs_purchased fields
