refactor: extract purchase/renewal flow to separate page

Move ~1900 lines of purchase/renewal logic from Subscription.tsx into
a new SubscriptionPurchase.tsx page at /subscription/purchase.

- Create SubscriptionPurchase.tsx with tariffs grid, classic mode wizard,
  switch preview modal, and promo handling
- Create PurchaseCTAButton.tsx with animated gradient border, state-aware
  colors and context-aware text
- Create subscriptionHelpers.ts with shared utilities
- Add CopyIcon to shared icons module
- Register /subscription/purchase route with lazy loading
- Update SubscriptionCardExpired and PromoOffersSection navigators
- Add CTA translation keys to ru.json and en.json
- Remove all scrollToExtend references

src/components/PromoOffersSection.tsx

@@ -156,7 +156,7 @@ export default function PromoOffersSection({ className = '' }: PromoOffersSectio
   };
 
   const handleUseNow = () => {
-    navigate('/subscription', { state: { scrollToExtend: true } });
+    navigate('/subscription/purchase');
   };
 
   const handleDeactivateClick = () => {