fix: keep keyboard update message alive instead of send-delete pattern

Previous approach (send \u200C then immediately delete it) lost the
reply keyboard because Telegram may not persist the keyboard from a
deleted message. Now we delete the OLD keyboard message and keep the
new one, ensuring the reply keyboard is always present and correct.

internal/bot/handlers.go

@@ -21,6 +21,7 @@ type Handler struct {
 	DB           *db.Store
 	AllowedUsers map[int64]bool
 	lastMsgTime  map[int64]time.Time
+	keyboardMsg  map[int64]int
 	mu           sync.Mutex
 }
 
@@ -30,6 +31,7 @@ func NewHandler(bot *tgbotapi.BotAPI, store *db.Store, allowed map[int64]bool) *
 		DB:           store,
 		AllowedUsers: allowed,
 		lastMsgTime:  make(map[int64]time.Time),
+		keyboardMsg:  make(map[int64]int),
 	}
 }
 
@@ -359,11 +361,19 @@ func (h *Handler) handleStart(msg *tgbotapi.Message) {
 }
 
 func (h *Handler) updateReplyKeyboard(chatID int64) {
+	h.mu.Lock()
+	oldID := h.keyboardMsg[chatID]
+	h.mu.Unlock()
+	if oldID != 0 {
+		h.Bot.Request(tgbotapi.NewDeleteMessage(chatID, oldID))
+	}
 	msg := tgbotapi.NewMessage(chatID, "\u200C")
 	msg.ReplyMarkup = h.smartKeyboard(chatID)
 	sent, err := h.Bot.Send(msg)
 	if err == nil {
-		h.Bot.Request(tgbotapi.NewDeleteMessage(chatID, sent.MessageID))
+		h.mu.Lock()
+		h.keyboardMsg[chatID] = sent.MessageID
+		h.mu.Unlock()
 	}
 }