feat(telegram): link the promo body @username to the Mini App deep link

The promo message body now renders "@<bot>" as an HTML text_link to the same ?startapp deep link the button uses (ParseMode HTML), so tapping the mention opens the seeded Mini App instead of the bot profile. Same payload (campaign start-param, else the forwarded /start payload) backs both the button and the mention.

platform/telegram/internal/promobot/promobot.go

@@ -11,6 +11,7 @@ package promobot
 import (
 	"cmp"
 	"context"
+	"html"
 	"net/url"
 	"strings"
 
@@ -112,13 +113,16 @@ func (t *Bot) handleStart(ctx context.Context, api *tgbot.Bot, update *models.Up
 	if update.Message.From != nil {
 		lang = update.Message.From.LanguageCode
 	}
-	text, button := promoText(lang, t.username)
+	// The configured campaign payload (a variant-seed deep link) takes precedence; absent
+	// one, fall back to forwarding any /start payload the user arrived with. The same
+	// payload backs both the inline button and the @username link in the body.
+	param := cmp.Or(t.startParam, startPayload(update.Message.Text))
+	text, button := promoText(lang, t.username, t.launchURL(param))
 	if _, err := api.SendMessage(ctx, &tgbot.SendMessageParams{
-		ChatID: update.Message.Chat.ID,
-		Text:   text,
-		// The configured campaign payload (a variant-seed deep link) takes precedence;
-		// absent one, fall back to forwarding any /start payload the user arrived with.
-		ReplyMarkup: t.launchMarkup(button, cmp.Or(t.startParam, startPayload(update.Message.Text))),
+		ChatID:      update.Message.Chat.ID,
+		Text:        text,
+		ParseMode:   models.ParseModeHTML,
+		ReplyMarkup: t.launchMarkup(button, param),
 	}); err != nil {
 		t.log.Warn("promo: reply to start failed", zap.Error(err))
 	}
@@ -169,11 +173,15 @@ func startPayload(text string) string {
 	return strings.TrimSpace(strings.TrimPrefix(text, cmd))
 }
 
-// promoText returns the localized message body and button label, naming the main bot
-// (Russian for a "ru" language code, English otherwise).
-func promoText(lang, username string) (text, button string) {
+// promoText returns the localized message body and button label. The body names the main
+// bot as a clickable @username whose link is the Mini App deep link (launchURL, the same
+// target as the button), so tapping the mention opens the seeded Mini App rather than the
+// bot profile. The body is sent with ParseMode HTML; only the link carries markup, so the
+// static sentences need no escaping. Russian for a "ru" language code, English otherwise.
+func promoText(lang, username, launchURL string) (text, button string) {
+	mention := `<a href="` + html.EscapeString(launchURL) + `">@` + html.EscapeString(username) + `</a>`
 	if strings.HasPrefix(strings.ToLower(lang), "ru") {
-		return "Откройте @" + username + " и выберите в настройках профиля нужный вариант игры.", "🤩 Хочу играть!"
+		return "Откройте " + mention + " и выберите в настройках профиля нужный вариант игры.", "🤩 Хочу играть!"
 	}
-	return "Open @" + username + " and choose your game variant in the profile settings.", "🤩 I want to play!"
+	return "Open " + mention + " and choose your game variant in the profile settings.", "🤩 I want to play!"
 }