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.ts

@@ -398,9 +398,22 @@ export function decodeWallet(buf: Uint8Array): Wallet {
     adsForever: w.adsForever(),
     adsPaidUntilMs: Number(w.adsPaidUntilMs()),
     hints: w.hints(),
+    rewardChips: w.rewardChips(),
   };
 }
 
+// encodeWalletReward wraps a watched rewarded video for crediting (POST /user/wallet/reward): the
+// per-view idempotency nonce and the raw VK ad result forwarded for the contour diagnostic.
+export function encodeWalletReward(nonce: string, diag: string): Uint8Array {
+  const b = new Builder(64);
+  const n = b.createString(nonce);
+  const d = b.createString(diag);
+  fb.WalletRewardRequest.startWalletRewardRequest(b);
+  fb.WalletRewardRequest.addNonce(b, n);
+  fb.WalletRewardRequest.addDiag(b, d);
+  return finish(b, fb.WalletRewardRequest.endWalletRewardRequest(b));
+}
+
 // 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));