feat(telegram,game): single bot + per-user variant preferences

Collapse the two per-language Telegram bots into one unified bot and
replace language-based variant gating with explicit per-user variant
preferences.

- Telegram: one bot; drop service_language and the supported_languages
  set everywhere (DB, account, auth, FlatBuffers Session wire, gateway,
  connector proto). The single bot renders chat and out-of-app push in
  the recipient's preferred_language; remove the game-language push
  routing override (notify Intent.Language / push Event.language).
- Preferences: new accounts.variant_preferences (text[], DB default
  {erudit_ru}, CHECK non-empty + subset of the three variants). Gates
  the New Game picker, vs-AI and the friend invitation the player
  creates, enforced server-side (HTTP 400 otherwise); an invited friend
  may still accept any variant. Edited on the Settings screen; variants
  are Erudit-first everywhere.
- Admin: drop the per-bot language selectors (broadcast / send-to-user)
  and the feedback channel_lang column/field.
- Env/CI: collapse TELEGRAM_BOT_TOKEN_{EN,RU}, TELEGRAM_GAME_CHANNEL_ID_{EN,RU},
  VITE_TELEGRAM_LINK{,_EN,_RU} and VITE_TELEGRAM_GAME_CHANNEL_NAME_{EN,RU}
  to single unsuffixed names; drop GATEWAY_DEFAULT_SUPPORTED_LANGUAGES.
- Docs updated (ARCHITECTURE, FUNCTIONAL + _ru, platform/telegram, gateway,
  backend, ui, UI_DESIGN, PRERELEASE).

The migration squash is deferred to a follow-up PR.

platform/telegram/cmd/telegram/main.go

@@ -67,36 +67,22 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 		logger.Warn("telemetry: start runtime metrics", zap.Error(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)
+	// The single bot validates launch data and delivers push/admin messages.
+	b, err := bot.New(bot.Config{
+		Token:      cfg.Token,
+		APIBaseURL: cfg.APIBaseURL,
+		TestEnv:    cfg.TestEnv,
+		MiniAppURL: cfg.MiniAppURL,
+	}, logger)
+	if err != nil {
+		return err
 	}
-	srv := connector.NewServer(runtimes, logger)
+	srv := connector.NewServer(connector.BotRuntime{
+		Sender:          b,
+		ChannelID:       cfg.GameChannelID,
+		InitValidator:   initdata.NewHMACValidator(cfg.Token),
+		WidgetValidator: loginwidget.NewHMACValidator(cfg.Token),
+	}, logger)
 
 	grpcServer := grpc.NewServer(grpc.StatsHandler(otelgrpc.NewServerHandler()))
 	telegramv1.RegisterTelegramServer(grpcServer, srv)
@@ -106,11 +92,9 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 		return err
 	}
 
-	// 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)
-	}
+	// 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)
 	go func() {
 		<-ctx.Done()
 		grpcServer.GracefulStop()
@@ -119,7 +103,6 @@ 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