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/i18n/en.ts

@@ -242,6 +242,11 @@ export const en = {
   'wallet.store': 'Store',
   'wallet.empty': 'The store is empty for now',
   'wallet.buy': 'Buy',
+  'wallet.rewardWatch': 'Watch an ad for {n} 🪙',
+  'wallet.rewardCta': 'Watch',
+  'wallet.rewardCredited': '+{n} 🪙 for watching',
+  'wallet.rewardCapped': "You've reached today's reward limit",
+  'wallet.rewardFailed': 'The ad could not be shown',
   'wallet.offer': 'Public offer',
   'wallet.platformNoBuy': 'Purchases are not available on this platform',
   'wallet.iosBlockedPre': 'Purchases on iOS are prohibited by Apple policy. Try the ',

ui/src/lib/i18n/ru.ts

@@ -242,6 +242,11 @@ export const ru: Record<MessageKey, string> = {
   'wallet.store': 'Магазин',
   'wallet.empty': 'Магазин пока пуст',
   'wallet.buy': 'Купить',
+  'wallet.rewardWatch': 'Ролик за {n} 🪙',
+  'wallet.rewardCta': 'Смотреть',
+  'wallet.rewardCredited': '+{n} 🪙 за просмотр',
+  'wallet.rewardCapped': 'Достигнут дневной лимит наград',
+  'wallet.rewardFailed': 'Не удалось показать ролик',
   'wallet.offer': 'Публичная оферта',
   'wallet.platformNoBuy': 'На данной платформе покупки невозможны',
   'wallet.iosBlockedPre': 'Покупки на iOS запрещены политикой Apple. Попробуйте воспользоваться ',