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/mock/client.ts

@@ -126,6 +126,7 @@ export class MockGateway implements GatewayClient {
     adsForever: false,
     adsPaidUntilMs: 0,
     hints: 5,
+    rewardChips: 5,
   };
   // The mock storefront: two chip-priced values (one cheap enough to draw direct only, one that
   // reaches into vk → the warning) and one RUB-priced chip pack (the direct-context method).
@@ -234,12 +235,20 @@ export class MockGateway implements GatewayClient {
     // the provider hand-off without leaving the app.
     return { orderId: 'mock-order-' + productId, redirectUrl: 'https://mock.local/robokassa?order=' + productId };
   }
+
+  async walletReward(_nonce: string, _diag: string): Promise<Wallet> {
+    // Mock rewarded credit: add the configured payout to the vk segment (no cap in the mock).
+    const vk = this.mockWallet.segments.find((s) => s.source === 'vk');
+    if (vk) vk.chips += this.mockWallet.rewardChips;
+    return this.cloneWallet();
+  }
   private cloneWallet(): Wallet {
     return {
       segments: this.mockWallet.segments.map((s) => ({ ...s })),
       adsForever: this.mockWallet.adsForever,
       adsPaidUntilMs: this.mockWallet.adsPaidUntilMs,
       hints: this.mockWallet.hints,
+      rewardChips: this.mockWallet.rewardChips,
     };
   }
   async fetchDict(variant: Variant, _version: string, opts?: { signal?: AbortSignal; reload?: boolean }): Promise<ArrayBuffer> {