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/cmd/telegram/main.go

@@ -67,19 +67,36 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 		logger.Warn("telemetry: start runtime metrics", zap.Error(err))
 	}
 
-	b, err := bot.New(bot.Config{
-		Token:      cfg.BotToken,
-		APIBaseURL: cfg.APIBaseURL,
-		TestEnv:    cfg.TestEnv,
-		MiniAppURL: cfg.MiniAppURL,
-	}, logger)
-	if err != nil {
-		return err
+	// One bot per configured service language; ValidateInitData tries each token and
+	// the push/admin methods route by language.
+	var bots []*bot.Bot
+	var runtimes []connector.BotRuntime
+	var langs []string
+	for _, lang := range config.Languages {
+		bc, ok := cfg.Bots[lang]
+		if !ok {
+			continue
+		}
+		b, err := bot.New(bot.Config{
+			Token:      bc.Token,
+			APIBaseURL: cfg.APIBaseURL,
+			TestEnv:    cfg.TestEnv,
+			MiniAppURL: cfg.MiniAppURL,
+		}, logger)
+		if err != nil {
+			return err
+		}
+		bots = append(bots, b)
+		runtimes = append(runtimes, connector.BotRuntime{
+			Language:        lang,
+			Sender:          b,
+			ChannelID:       bc.GameChannelID,
+			InitValidator:   initdata.NewHMACValidator(bc.Token),
+			WidgetValidator: loginwidget.NewHMACValidator(bc.Token),
+		})
+		langs = append(langs, lang)
 	}
-	srv := connector.NewServer(
-		initdata.NewHMACValidator(cfg.BotToken),
-		loginwidget.NewHMACValidator(cfg.BotToken),
-		b, cfg.GameChannelID, logger)
+	srv := connector.NewServer(runtimes, logger)
 
 	grpcServer := grpc.NewServer(grpc.StatsHandler(otelgrpc.NewServerHandler()))
 	telegramv1.RegisterTelegramServer(grpcServer, srv)
@@ -89,9 +106,11 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 		return err
 	}
 
-	// The long-poll loop and the gRPC server run together; cancelling the context
-	// stops the bot loop and gracefully drains the gRPC server.
-	go b.Run(ctx)
+	// The long-poll loops and the gRPC server run together; cancelling the context
+	// stops every bot loop and gracefully drains the gRPC server.
+	for _, b := range bots {
+		go b.Run(ctx)
+	}
 	go func() {
 		<-ctx.Done()
 		grpcServer.GracefulStop()
@@ -100,6 +119,7 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	logger.Info("telegram connector starting",
 		zap.String("grpc_addr", cfg.GRPCAddr),
 		zap.String("miniapp_url", cfg.MiniAppURL),
+		zap.Strings("languages", langs),
 		zap.Bool("test_env", cfg.TestEnv))
 	if err := grpcServer.Serve(lis); err != nil && !errors.Is(err, grpc.ErrServerStopped) {
 		return err