Stage 15: dual Telegram bots & language-gated variants

Service-agnostic refinement of the owner's idea: the sign-in service returns a
set of supported game languages with the user identity, and the lobby gates the
New Game variant choice by it (en -> English; ru -> Russian + Эрудит).

- Connector hosts two bots in one container (one per service language, each its
  own token + game channel; the same telegram_id spans both). ValidateInitData
  tries each token and returns the validating bot's service_language +
  supported_languages. Per-language config (TELEGRAM_BOT_TOKEN_EN/_RU, channels).
- supported_languages rides the Session (fbs, session-scoped, not persisted); the
  UI offers only the matching variants on New Game — gating only the START of a
  new game (auto-match + friend invite), not accept/open/play; backend does not
  enforce.
- service_language persisted (accounts.service_language, migration 00010, written
  every login, last-login-wins) and routes the user-facing Notify push back
  through the right bot (push-target coalesces with preferred_language).
- Admin SendToUser/SendToGameChannel gain an operator-chosen language selector in
  the console (unrelated to ValidateInitData).
- Non-Telegram logins carry the gateway default set
  (GATEWAY_DEFAULT_SUPPORTED_LANGUAGES, all variants).

Wire (committed regen): ValidateInitDataResponse +service_language
+supported_languages; Session +supported_languages; SendToUser/SendToGameChannel
+language. Docs (ARCHITECTURE/FUNCTIONAL/_ru/READMEs) + PLAN updated; stage marked done.

platform/telegram/README.md

@@ -1,9 +1,22 @@
 # scrabble/platform/telegram — Telegram connector
 
 The Telegram platform side-service. It is the **only** component that holds the bot
-token: it runs the Bot API long-poll loop (Mini App launch + deep-links) and serves
-the connector gRPC API that the gateway and backend call over the trusted internal
-network. See [`docs/ARCHITECTURE.md`](../../docs/ARCHITECTURE.md) §1/§3/§10/§12.
+tokens: it runs a Bot API long-poll loop **per service language** (Mini App launch +
+deep-links) and serves the connector gRPC API that the gateway and backend call over
+the trusted internal network. See
+[`docs/ARCHITECTURE.md`](../../docs/ARCHITECTURE.md) §1/§3/§10/§12.
+
+## Service languages (dual bots)
+
+The connector hosts **one bot per service language** (`en`, `ru`) — each its own
+token + game channel, configured by the `*_EN` / `*_RU` env vars; at least one is
+required. The **same Telegram user id spans both bots**. `ValidateInitData` tries
+each bot's token in turn (none validates ⇒ invalid) and reports which bot validated:
+its **`service_language`** (persisted by the backend to route the user's later push)
+and its **`supported_languages`** set (which the UI gates the New Game variant choice
+by — `en` → English, `ru` → Russian + Эрудит). The user-facing `Notify` routes by the
+recipient's persisted service language; the admin `SendToUser` / `SendToGameChannel`
+route by an **operator-chosen** `language` (unrelated to login).
 
 ## Responsibilities
 
@@ -13,7 +26,8 @@ network. See [`docs/ARCHITECTURE.md`](../../docs/ARCHITECTURE.md) §1/§3/§10/
   backend internal API — so the bot token never leaves this process.
 - **Out-of-app push.** `Notify` renders a backend push event (your_turn, nudge,
   match_found, and the invitation / friend_request notify sub-kinds) into a
-  localized message with a Mini App launch button and sends it. The gateway calls it
+  localized message with a Mini App launch button and sends it **through the bot for
+  the request's `language`** (the recipient's service language). The gateway calls it
   **only** for a recipient with no live in-app stream and the
   `notifications_in_app_only` flag off, so the platform push never duplicates in-app
   delivery.
@@ -21,7 +35,8 @@ network. See [`docs/ARCHITECTURE.md`](../../docs/ARCHITECTURE.md) §1/§3/§10/
   launch button; a deep-link payload routes the launch to a game / invitation /
   friend code.
 - **Admin messaging** (wired in Stage 10). `SendToUser` and `SendToGameChannel` send
-  arbitrary text to one user or the configured game channel.
+  arbitrary text to one user or a game channel through the bot the request selects by
+  `language` (an operator choice in the admin console).
 
 The generic methods (`Notify`, `SendToUser`, `SendToGameChannel`) address a
 recipient by the identity `external_id` (as in the backend `identities` table), so a
@@ -56,12 +71,14 @@ The bot turns a `/start <payload>` or a notification target into a launch-button
 
 | Env var | Default | Meaning |
 | --- | --- | --- |
-| `TELEGRAM_BOT_TOKEN` | — (required) | Bot API token + the initData HMAC secret |
-| `TELEGRAM_MINIAPP_URL` | — (required) | Mini App HTTPS origin (BotFather-registered) |
+| `TELEGRAM_BOT_TOKEN_EN` | — | English bot's API token + initData HMAC secret |
+| `TELEGRAM_BOT_TOKEN_RU` | — | Russian bot's API token + initData HMAC secret (≥ 1 of EN/RU required) |
+| `TELEGRAM_GAME_CHANNEL_ID_EN` | — | English bot's game channel chat id for `SendToGameChannel` |
+| `TELEGRAM_GAME_CHANNEL_ID_RU` | — | Russian bot's game channel chat id |
+| `TELEGRAM_MINIAPP_URL` | — (required) | Mini App HTTPS origin, shared by all bots (BotFather-registered) |
 | `TELEGRAM_GRPC_ADDR` | `:9091` | connector gRPC listen address |
 | `TELEGRAM_API_BASE_URL` | `https://api.telegram.org` | Bot API host override (mock / self-hosted) |
 | `TELEGRAM_TEST_ENV` | `false` | route to the Bot API **test environment** (`/bot<token>/test/METHOD`) |
-| `TELEGRAM_GAME_CHANNEL_ID` | — | game channel chat id for `SendToGameChannel` |
 | `TELEGRAM_LOG_LEVEL` | `info` | zap log level |
 | `TELEGRAM_SERVICE_NAME` | `scrabble-telegram` | OpenTelemetry `service.name` |
 | `TELEGRAM_OTEL_TRACES_EXPORTER` | `none` | `none`, `stdout` or `otlp` (gRPC; endpoint from `OTEL_EXPORTER_OTLP_*`) |
@@ -76,7 +93,7 @@ builds `<host>/bot<token>/<method>`).
 ```sh
 go build ./platform/telegram/...
 go test ./platform/telegram/...        # unit tests use an httptest fake Bot API
-go run ./platform/telegram/cmd/telegram # needs a real TELEGRAM_BOT_TOKEN
+go run ./platform/telegram/cmd/telegram # needs a real TELEGRAM_BOT_TOKEN_EN or _RU
 ```
 
 ## Deploy