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/codec.ts

@@ -39,6 +39,7 @@ import type {
   MoveResult,
   Profile,
   Wallet,
+  WalletOrder,
   WalletSegment,
   Catalog,
   CatalogProduct,
@@ -373,6 +374,15 @@ export function encodeWalletBuy(productId: string): Uint8Array {
   return finish(b, fb.WalletBuyRequest.endWalletBuyRequest(b));
 }
 
+// encodeWalletOrder wraps the pack id for a money order (POST /user/wallet/order).
+export function encodeWalletOrder(productId: string): Uint8Array {
+  const b = new Builder(64);
+  const pid = b.createString(productId);
+  fb.WalletOrderRequest.startWalletOrderRequest(b);
+  fb.WalletOrderRequest.addProductId(b, pid);
+  return finish(b, fb.WalletOrderRequest.endWalletOrderRequest(b));
+}
+
 // decodeWallet reads the wallet payload: the context-visible chip segments and the
 // context-applicable benefits.
 export function decodeWallet(buf: Uint8Array): Wallet {
@@ -391,6 +401,12 @@ export function decodeWallet(buf: Uint8Array): Wallet {
   };
 }
 
+// decodeWalletOrder reads the created order: its id and the provider launch URL the client opens.
+export function decodeWalletOrder(buf: Uint8Array): WalletOrder {
+  const o = fb.WalletOrderResponse.getRootAsWalletOrderResponse(new ByteBuffer(buf));
+  return { orderId: s(o.orderId()), redirectUrl: s(o.redirectUrl()) };
+}
+
 // decodeCatalog reads the storefront payload: the context-visible products, each a chip-priced
 // value or a chip pack priced in the context's payment method, with its atom composition.
 export function decodeCatalog(buf: Uint8Array): Catalog {