feat(ads): rewarded video (VK) — client-attested credit + daily/hourly caps

The first ads slice: a voluntary rewarded video credits chips. VK Mini App ads
(VKWebAppShowNativeAds) expose only a client-side watch result — no
server-to-server verify — so the credit is client-attested, guarded by a server
daily + hourly cap (config reward_daily_cap / reward_hourly_cap, default 50 / 10).
The caps are both anti-abuse (bounding a forger who skips the ad and calls the
endpoint directly) and an economic conversion lever (limiting free chips so a
player who wants more buys). D29 amended to VK's reality.

Backend: CreditReward (VK-only, order-less, idempotent on a client nonce, floored
by the caps; payout from config rewarded_payout_chips, default 0 = off) + the
wallet.reward edge op returning the updated wallet (reward_chips gates the
"watch for chips" CTA). Additive migration (two config columns).

Client: the ads-network abstraction (lib/ads.ts, VK impl) + the VK bridge
(vkRewardedReady / vkShowRewarded) + the Wallet CTA + i18n. A contour test stub
(VITE_ADS_STUB -> a toast instead of a real ad; prod always real) and a temporary
diagnostic that logs the raw VK data, so we confirm on the contour exactly what
VK returns (harden to signature-verify if it carries one).

Tests: backend integration (credit, nonce idempotency, hourly cap, disabled,
non-VK refusal) + codec unit (reward wire). Docs: PAYMENTS(+ru) §10, D29 amend,
PLAN E6. Bundle: shared budget 30->31 (reward i18n strings).

ui/src/lib/codec.test.ts

@@ -15,6 +15,7 @@ import {
   decodeOutgoingList,
   decodeProfile,
   decodeWallet,
+  encodeWalletReward,
   decodeCatalog,
   encodeWalletBuy,
   encodeWalletOrder,
@@ -66,6 +67,7 @@ describe('codec', () => {
     fb.Wallet.addAdsForever(b, false);
     fb.Wallet.addAdsPaidUntilMs(b, BigInt(1_700_000_000_000));
     fb.Wallet.addHints(b, 5);
+    fb.Wallet.addRewardChips(b, 7);
     b.finish(fb.Wallet.endWallet(b));
 
     const w = decodeWallet(b.asUint8Array());
@@ -73,6 +75,15 @@ describe('codec', () => {
     expect(w.adsForever).toBe(false);
     expect(w.adsPaidUntilMs).toBe(1_700_000_000_000);
     expect(w.hints).toBe(5);
+    expect(w.rewardChips).toBe(7);
+  });
+
+  it('round-trips the wallet reward request (nonce + diag)', () => {
+    const req = fb.WalletRewardRequest.getRootAsWalletRewardRequest(
+      new ByteBuffer(encodeWalletReward('nonce-9', '{"result":true}')),
+    );
+    expect(req.nonce()).toBe('nonce-9');
+    expect(req.diag()).toBe('{"result":true}');
   });
 
   it('round-trips the wallet order request and response', () => {