display date in user's selected calendar on main menu and reports

buildStatusText and buildDailyReport now use formatDateForCalendar
to convert the stored Gregorian date to the user's calendar type
(jalali/hijri/gregorian).

internal/bot/dateutil.go

@@ -276,3 +276,17 @@ func parseGregorianDateKey(key string) (int, int, int) {
 	fmt.Sscanf(key, "%04d-%02d-%02d", &y, &m, &d)
 	return y, m, d
 }
+
+func formatDateForCalendar(date, calType string) string {
+	y, m, d := parseGregorianDateKey(date)
+	switch calType {
+	case "jalali":
+		jy, jm, jd := gregorianToJalali(y, m, d)
+		return fmt.Sprintf("%04d-%02d-%02d", jy, jm, jd)
+	case "hijri":
+		hy, hm, hd := gregorianToHijri(y, m, d)
+		return fmt.Sprintf("%04d-%02d-%02d", hy, hm, hd)
+	default:
+		return date
+	}
+}