feat: podpora dark mode

client/src/App.tsx

@@ -436,7 +436,7 @@ function App() {
               <span title='Předchozí den'>
                 <FontAwesomeIcon icon={faChevronLeft} style={{ cursor: "pointer", visibility: dayIndex > 0 ? "initial" : "hidden" }} onClick={() => handleDayChange(dayIndex - 1)} />
               </span>
-              <h1 className='title' style={{ color: dayIndex === data.todayDayIndex ? 'black' : 'gray' }}>{data.date}</h1>
+              <h1 className={`title ${dayIndex !== data.todayDayIndex ? 'text-muted' : ''}`}>{data.date}</h1>
               <span title="Následující den">
                 <FontAwesomeIcon icon={faChevronRight} style={{ cursor: "pointer", visibility: dayIndex < 4 ? "initial" : "hidden" }} onClick={() => handleDayChange(dayIndex + 1)} />
               </span>