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).

.gitea/workflows/ci.yaml

@@ -407,6 +407,9 @@ jobs:
           # the VK ID redirect URL is derived from PUBLIC_BASE_URL in the run step below.
           VITE_VK_APP_LINK: ${{ vars.VITE_VK_APP_LINK }}
           VITE_VK_APP_ID: ${{ vars.VITE_VK_APP_ID }}
+          # Rewarded-ad test stub: set TEST_VITE_ADS_STUB=1 to swap real ads for a toast on the
+          # contour (empty = real ads, for capturing the real VK ad result). Prod never sets it.
+          VITE_ADS_STUB: ${{ vars.TEST_VITE_ADS_STUB }}
           # VITE_GATEWAY_URL omitted: the SPA is served same-origin, so it stays the
           # compose ":-" empty default. Other unset vars likewise fall to their defaults.
           POSTGRES_DB: ${{ vars.TEST_POSTGRES_DB }}