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/scripts/bundle-size.mjs

@@ -7,7 +7,9 @@
 //
 // Three independent gates on the natural chunk boundaries, each with realistic headroom:
 //   - app entry (main):     the app's own code; grows with features.
-//   - shared (svelte+i18n):  near-static framework runtime; only drifts on a dep/Svelte bump.
+//   - shared (svelte+i18n):  the framework runtime plus the flat i18n map; drifts on a dep/Svelte
+//                            bump and, slightly, as feature copy adds i18n keys (raised to 31 for
+//                            the rewarded-ad strings).
 //   - landing own:           the landing's own code; kept minimal.
 // Today ~74 KB (app entry) + ~23 KB (shared) = ~97 KB for the app; the landing's own chunk is
 // ~2 KB. Lazy-loading was analysed and rejected (no total-size win — every chunk still
@@ -32,7 +34,7 @@ const DIST = 'dist';
 // Telegram Stars openInvoice / VK order-box launch and the per-button in-flight state ride the same
 // always-loaded Wallet screen. The heavy parts — the dict loader, the move generator and the preload
 // orchestration — still stay in lazy chunks. Scoped CSS lands in the CSS chunk, not this JS budget.
-const BUDGET = { app: 125, shared: 30, landing: 5 };
+const BUDGET = { app: 125, shared: 31, landing: 5 };
 
 // gzipped returns the gzipped byte size of a built asset, or 0 when the reference is not a
 // local file (e.g. the Telegram SDK loaded from a CDN) or is missing.