feat(ui): wire the chip-pack purchase to Robokassa

Replace the disabled "Soon" pack action with a real purchase: the Wallet opens a
money order (wallet.order) and sends the player to the provider's hosted-payment
page (window.open via openExternalUrl); the chips are credited later by the
verified server callback. Add a public-offer link under the packs (paying
accepts the offer). Codec order round-trip unit test + a mock-e2e purchase test;
the Google Play stub and the chip-spend paths are unchanged.

ui/src/lib/i18n/en.ts

@@ -242,7 +242,7 @@ export const en = {
   'wallet.store': 'Store',
   'wallet.empty': 'The store is empty for now',
   'wallet.buy': 'Buy',
-  'wallet.soon': 'Soon',
+  'wallet.offer': 'Public offer',
   'wallet.gpStub': 'To buy chips, install the RuStore build.',
   'wallet.cur.RUB': '₽',
   'wallet.cur.VOTE': 'votes',