feat(vk): embed the game as a VK Mini App

Mirror the Telegram Mini App wrapper for VK: the SPA loads at a new /vk/
entry, authenticates from VK's signed launch parameters, and provisions a
'vk' platform identity — the minimum to run the game in VK test mode.

- Gateway verifies the launch signature in-process (internal/vkauth:
  HMAC-SHA256 over the sorted vk_* params under GATEWAY_VK_APP_SECRET,
  base64url) — a pure offline check, no side-service. New auth.vk op
  (gated on the secret), backendclient.VKAuth, /vk/ SPA mount.
- Backend: KindVK + ProvisionVK/vkSeed, /sessions/vk handler, identity
  kind widened to include 'vk' (migration 00005, expand-contract).
- UI: src/lib/vk.ts (VK Bridge, lazy-imported), bootVK + the /vk/ boot
  dispatch, encodeVKLogin + authVK across transport/client/mock. VK omits
  the name from the signed params, so the client reads it via
  VKWebAppGetUserInfo as an unsigned display seed.
- Deploy: /vk in the edge Caddyfile, GATEWAY_VK_APP_SECRET wired through
  compose + .env.example + CI (TEST_) + prod-deploy (PROD_).
- Admin console: surface the VK user id (link to the VK profile) next to
  the Telegram id on the user card.
- Docs: ARCHITECTURE §12/§13, FUNCTIONAL (+ _ru), gateway README; VK
  integration reference under .claude/.

Signature algorithm verified against dev.vk.com plus independent Node/Python
references and a %2C edge-case vector.

docs/ARCHITECTURE.md

@@ -149,11 +149,18 @@ arrive from a platform rather than completing a mandatory registration).
 
 - The gateway validates the originating credential **once** — Telegram `initData`
   (delegated to the **validator's** `ValidateInitData` RPC, which holds the bot token —
-  the HMAC secret — so it never reaches the gateway), an email-code login, or a guest
+  the HMAC secret — so it never reaches the gateway), a **VK Mini App** launch (verified
+  **in-process** by `gateway/internal/vkauth`: HMAC-SHA256 over the signed `vk_*` params
+  under the VK app's protected key `GATEWAY_VK_APP_SECRET`, base64url — a pure offline check,
+  as VK signing needs no API round-trip, so no side-service), an email-code login, or a guest
   bootstrap — then mints a **thin opaque server session token** (`session_id`). First
-  Telegram contact seeds the new account's language (from the launch `language_code`)
-  and display name (§4). The validator runs on the main host and never reaches the Bot
-  API, so login does not depend on Telegram or the remote bot being up (§10, §12).
+  Telegram/VK contact seeds the new account's language (Telegram's `language_code` / VK's
+  `vk_language`) and display name (§4; VK omits the name from the signed params, so the client
+  reads it via `VKWebAppGetUserInfo` as an unsigned, cosmetic seed). The validator runs on the
+  main host and never reaches the Bot API, so login does not depend on Telegram or the remote
+  bot being up (§10, §12). VK launch params carry no built-in expiry (unlike Telegram's
+  `auth_date`), so freshness is not enforced — the minted session is the short-lived credential,
+  and a replay only re-authenticates the same `vk_user_id`.
 - **Single bot.** The platform side-service runs **one bot** (one token + one optional
   game channel), split into a home **validator** and a remote **bot** that share the
   token. `ValidateInitData` (the validator) validates `initData` against that single
@@ -1046,10 +1053,11 @@ a dedicated redeem sub-limit or a longer code is the hardening step if abuse app
 Single public origin, path-routed. The Vite build has two entries: a lightweight
 **landing page** and the game **SPA**. The gateway **embeds** the SPA build
 (`go:embed`, baked in by a node stage in `gateway/Dockerfile`) and serves it at
-`/app/` (web) and `/telegram/` (the Telegram Mini App; on that path without sign-in data
+`/app/` (web), `/telegram/` (the Telegram Mini App; on that path without sign-in data
 — no `initData` — the client renders a compact, shareable launch-diagnostic screen instead
-of redirecting away); a stray hit on the gateway's `/`
-308-redirects to `/app/`. The **landing** ships in its own static container: the
+of redirecting away) and `/vk/` (the VK Mini App; the client reads the signed `vk_*` launch
+parameters from the URL and the gateway verifies them in-process — §12); a stray hit on the
+gateway's `/` 308-redirects to `/app/`. The **landing** ships in its own static container: the
 `landing` target of `gateway/Dockerfile` (caddy:2-alpine + the same Vite build,
 `deploy/landing/Caddyfile`) serves it at `/`, so stray public traffic is absorbed by
 static file serving and never reaches the Go edge. Hash-named `/assets/*` are served
@@ -1058,7 +1066,7 @@ static file serving and never reaches the Go edge. Hash-named `/assets/*` are se
 in-compose **caddy** is the contour's edge: it owns a single `/_gm` Basic-Auth and
 routes `/_gm/grafana/*` to **Grafana** (anonymous-admin, so the one shared login gates
 it with no per-user Grafana accounts) and the rest of `/_gm/*` to the backend-rendered
-**admin console**; `/app/`, `/telegram/` and the Connect path go to the gateway; the
+**admin console**; `/app/`, `/telegram/`, `/vk/` and the Connect path go to the gateway; the
 catch-all — notably the landing at `/` — goes to the landing container. The
 **Telegram validator** runs as a separate container with **no public ingress**,
 answering only internal gRPC (HMAC, no Telegram egress). The **Telegram bot** holds

docs/FUNCTIONAL.md

@@ -22,7 +22,7 @@ costs nothing when the rack has no legal move. The word-check accepts only the
 variant's alphabet, remembers answers within the session and rate-limits repeats.
 A public **landing page** at the site root introduces the game, switches language and
 theme, and links to the matching per-language Telegram channel; the game itself runs at
-`/app/` (web) and `/telegram/` (the Telegram Mini App). The landing's theme is ephemeral
+`/app/` (web), `/telegram/` (the Telegram Mini App) and `/vk/` (the VK Mini App). The landing's theme is ephemeral
 (it follows the system scheme, not the saved preference); its language choice is saved.
 
 ### Identity & sessions
@@ -35,6 +35,10 @@ the device safe-area, and — on first contact — seeds the new account's inter
 language from the Telegram client. If a launch cannot reach the backend (for example during a
 deployment), the Mini App retries quietly and then shows a small "couldn't load" screen with a
 **Retry** button, rather than dropping to the web sign-in, which has no place inside Telegram.
+A **VK Mini App** launch works the same way: it authenticates from VK's signed launch parameters
+(verified by the gateway), and on first contact seeds the new account's interface language from
+`vk_language` and its display name from the VK profile (read on the client, since VK does not put
+the name in the signed launch). The same quiet-retry "couldn't load" screen applies inside VK.
 Telegram runs a **single bot**: every player uses
 the same bot, and all of its chat and out-of-app notifications are written in the
 player's own **interface language** (en/ru). A separate optional **promo bot** can run alongside the

docs/FUNCTIONAL_ru.md

@@ -23,7 +23,7 @@ top-1 подсказку, безлимитную проверку слова с
 и ограничивает частоту повторов.
 Публичная **посадочная страница** в корне сайта представляет игру, переключает язык и
 тему и ведёт в соответствующий по-язычный Telegram-канал; сама игра живёт по адресам
-`/app/` (веб) и `/telegram/` (Telegram Mini App). Тема на странице эфемерна (берётся из
+`/app/` (веб), `/telegram/` (Telegram Mini App) и `/vk/` (VK Mini App). Тема на странице эфемерна (берётся из
 системной настройки, а не из сохранённой), выбор языка сохраняется.
 
 ### Личность и сессии
@@ -37,7 +37,11 @@ Mini App** авторизует по подписанным `initData` плат
 языку Telegram-клиента. Если запуск не может достучаться до бэкенда (например, во время
 деплоя), Mini App тихо повторяет попытки, а затем показывает небольшой экран «не удалось
 загрузить» с кнопкой **Повторить**, вместо того чтобы сбрасывать на веб-вход, которому внутри
-Telegram не место. Telegram держит **единого бота**: все игроки пользуются одним
+Telegram не место. Запуск **VK Mini App** работает так же: авторизует по подписанным
+launch-параметрам VK (их проверяет gateway), и при первом контакте задаёт язык интерфейса
+нового аккаунта по `vk_language`, а отображаемое имя — по профилю VK (читается на клиенте,
+так как VK не кладёт имя в подписанный запуск). Тот же экран тихого повтора «не удалось
+загрузить» действует и внутри VK. Telegram держит **единого бота**: все игроки пользуются одним
 и тем же ботом, а весь его чат и внеприложенческие уведомления пишутся на **языке
 интерфейса** самого игрока (en/ru). Рядом с основным может работать отдельный опциональный
 **промо-бот** — его единственная задача отвечать на `/start` коротким сообщением и кнопкой,