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/client.ts

@@ -35,6 +35,7 @@ import type {
   Variant,
   WordCheckResult,
   Wallet,
+  WalletOrder,
   Catalog,
 } from './model';
 
@@ -147,6 +148,9 @@ export interface GatewayClient {
   /** walletBuy spends chips on a chip-priced value and returns the updated wallet. Gate-checked
    *  server-side: an untrusted/frozen context or an insufficient balance is refused. */
   walletBuy(productId: string): Promise<Wallet>;
+  /** walletOrder opens a money order to fund a chip pack and returns the provider launch URL the
+   *  client opens; chips are credited later, by the verified server callback. Direct rail only. */
+  walletOrder(productId: string): Promise<WalletOrder>;
 
   // --- friends ---
   friendsList(): Promise<AccountRef[]>;