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.test.ts

@@ -17,6 +17,8 @@ import {
   decodeWallet,
   decodeCatalog,
   encodeWalletBuy,
+  encodeWalletOrder,
+  decodeWalletOrder,
   decodeSession,
   decodeFeedbackState,
   decodeFeedbackUnread,
@@ -73,6 +75,25 @@ describe('codec', () => {
     expect(w.hints).toBe(5);
   });
 
+  it('round-trips the wallet order request and response', () => {
+    // order request: pack id survives the wire
+    const req = fb.WalletOrderRequest.getRootAsWalletOrderRequest(new ByteBuffer(encodeWalletOrder('pack-7')));
+    expect(req.productId()).toBe('pack-7');
+
+    // order response: the created id and the provider launch URL decode back
+    const b = new Builder(64);
+    const oid = b.createString('order-123');
+    const url = b.createString('https://pay.example/abc');
+    fb.WalletOrderResponse.startWalletOrderResponse(b);
+    fb.WalletOrderResponse.addOrderId(b, oid);
+    fb.WalletOrderResponse.addRedirectUrl(b, url);
+    b.finish(fb.WalletOrderResponse.endWalletOrderResponse(b));
+
+    const order = decodeWalletOrder(b.asUint8Array());
+    expect(order.orderId).toBe('order-123');
+    expect(order.redirectUrl).toBe('https://pay.example/abc');
+  });
+
   it('round-trips the catalog view (value + pack)', () => {
     const b = new Builder(256);