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/locales/en.json

@@ -318,6 +318,11 @@
     "price": "Price",
     "noSubscription": "You don't have an active subscription",
     "getSubscription": "Get Subscription",
+    "cta": {
+      "expiredHint": "Choose a plan and pay",
+      "trialHint": "More traffic and devices",
+      "activeHint": "Renewal and plan change"
+    },
     "connectionInfo": "Connection Info",
     "copyLink": "Copy Link",
     "copied": "Copied!",