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).

PLAN.md

@@ -35,7 +35,7 @@ status — without re-deriving decisions.
 | E3 | Wallet UI | 1 | DONE |
 | E4 | Durability (PITR) | 2 | DONE |
 | E5 | Payment intake | 2 | DONE |
-| E6 | Ads | 2 | TODO |
+| E6 | Ads | 2 | WIP |
 | E7 | Admin & reports | 2 | TODO |
 | E8 | Guest limits | — | TODO |
 | E9 | Tournament fee | future | TODO |
@@ -618,9 +618,27 @@ force-recreate when the Caddyfile changes.
 
 ## E6 — Ads
 
-**Status:** TODO · **Release 2** · depends on: E2 (chips), E5 (rewarded credits via intake) ·
+**Status:** WIP · **Release 2** · depends on: E2 (chips), E5 (rewarded credits via intake) ·
 mechanics: PAYMENTS §10.
 
+**Delivery & baked decisions.** Shipped as a linear PR stack (owner's choice): **rewarded first**,
+then interstitial. Baked: the interstitial cooldowns already exist in `payments.config` (E0) and the
+per-origin banner suppression is already done (E2 `AdFree`), so E6 is the two ad DISPLAY paths + the
+rewarded credit. **VK reality (checked live in the VK docs via Playwright):** VK Mini App ads
+(`VKWebAppShowNativeAds`, both `reward` and `interstitial`) expose **only a client-side `data.result`
+boolean** — no server verify, no signature. So **D29 is amended**: rewarded is **client-attested**,
+guarded by a server **daily + hourly cap** (config `reward_daily_cap` / `reward_hourly_cap`, default
+50 / 10) that is both anti-abuse and an economic conversion lever (limits free chips so players buy);
+the cooldown state for the interstitial is **client-mirrored** (owner's pick). Delivered on
+`feature/ads-rewarded` (the **rewarded** slice): the ads-network abstraction (`ui/src/lib/ads.ts`, VK
+impl) + the VK bridge (`vkRewardedReady` / `vkShowRewarded`), the 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
+(with `reward_chips` gating the "watch for chips" CTA), and a **contour test stub** (`VITE_ADS_STUB` →
+a toast instead of a real ad; prod always real). A temporary diagnostic logs the raw VK `data` so we
+confirm on the contour exactly what VK returns (harden to signature-verify if it carries one). The
+legacy `paid_account` / `hint_balance` drop (D31) and the **interstitial** are the next slice.
+
 **Goal.** VK video ads: the post-move interstitial (frequency-gated) and the rewarded video
 (credits chips via server verify), plus extending the existing banner suppression to
 per-origin.