feat: add inline keyboard, /start command, and callback handlers

- Show main menu with Clock In/Out, Report, Export, Remote, Day Off buttons
- Each action result includes a 'Back to Menu' button
- Handle callback queries alongside text commands
- Delete stale webhook before switching to polling
- Log i18n initialization error instead of silently ignoring it

cmd/bot/main.go

@@ -33,7 +33,10 @@ func main() {
 		log.Fatal(err)
 	}
 
-	translator, _ := i18n.NewTranslator("en")
+	translator, err := i18n.NewTranslator("en")
+	if err != nil {
+		log.Fatal("i18n: ", err)
+	}
 
 	handler := bot.NewHandler(botAPI, dbStore, translator)
 
@@ -41,7 +44,10 @@ func main() {
 	if webhookURL != "" {
 		startWebhook(botAPI, handler, webhookURL)
 	} else {
-		// Fallback to long‑polling
+		// Fallback to long‑polling — remove any stale webhook first
+		if _, err := botAPI.Request(tgbotapi.DeleteWebhookConfig{}); err != nil {
+			log.Printf("DeleteWebhook: %v", err)
+		}
 		u := tgbotapi.NewUpdate(0)
 		u.Timeout = 30
 		updates := botAPI.GetUpdatesChan(u)
@@ -49,6 +55,9 @@ func main() {
 			if update.Message != nil {
 				handler.HandleMessage(update)
 			}
+			if update.CallbackQuery != nil {
+				handler.HandleCallback(update)
+			}
 		}
 	}
 }