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).

gateway/Dockerfile

@@ -29,6 +29,9 @@ ARG VITE_VK_APP_ID=
 ARG VITE_VK_ID_REDIRECT_URL=
 ARG VITE_GATEWAY_URL=
 ARG VITE_APP_VERSION=
+# VITE_ADS_STUB=1 substitutes a toast stub for real ads (the test contour only); production leaves it
+# empty so it always shows real ads (a failed real ad must not credit).
+ARG VITE_ADS_STUB=
 ENV VITE_TELEGRAM_BOT_ID=$VITE_TELEGRAM_BOT_ID \
     VITE_TELEGRAM_LINK=$VITE_TELEGRAM_LINK \
     VITE_TELEGRAM_GAME_CHANNEL_NAME=$VITE_TELEGRAM_GAME_CHANNEL_NAME \
@@ -36,7 +39,8 @@ ENV VITE_TELEGRAM_BOT_ID=$VITE_TELEGRAM_BOT_ID \
     VITE_VK_APP_ID=$VITE_VK_APP_ID \
     VITE_VK_ID_REDIRECT_URL=$VITE_VK_ID_REDIRECT_URL \
     VITE_GATEWAY_URL=$VITE_GATEWAY_URL \
-    VITE_APP_VERSION=$VITE_APP_VERSION
+    VITE_APP_VERSION=$VITE_APP_VERSION \
+    VITE_ADS_STUB=$VITE_ADS_STUB
 
 # Install with the lockfile first (the workspace file carries pnpm's build-script
 # approval for esbuild), then build. Committed src/gen/ means no codegen here.