fix(frontend): prevent RangeError in TimeAdjuster and add validation to SleepButton

frontend/src/components/tracker/SleepButton.tsx

@@ -10,6 +10,10 @@ const SleepButton: React.FC<SleepButtonProps> = ({ time }) => {
   const isSleeping = !!activeSession;
 
   const handleClick = async () => {
+    if (!time) {
+      alert('Please select a valid time.');
+      return;
+    }
     try {
       if (isSleeping && activeSession?.id) {
         await endSession({ sessionId: activeSession.id, endTime: time });

frontend/src/utils/time.ts

@@ -90,6 +90,9 @@ export function formatDateTime(date: Date | string): string {
  */
 export function toUTCFromLocalInput(inputValue: string): string {
   const d = new Date(inputValue);
+  if (isNaN(d.getTime())) {
+    return "";
+  }
   return d.toISOString();
 }