Fix timezone issue: display booking slots in UTC

- Changed formatTime() to use UTC methods instead of toLocaleTimeString()
- Prevents timezone conversion when displaying booking slots
- Now admin sets 9-17 and user sees 9-17, regardless of timezone
- Fixes 1-hour offset issue when user timezone differs from UTC

frontend/app/utils/date.ts

@@ -13,15 +13,15 @@ export function formatDate(d: Date): string {
 }
 
 /**
- * Format time from ISO string to HH:MM format.
+ * Format time from ISO string to HH:MM format in UTC.
+ * Uses UTC to avoid timezone conversion issues when displaying booking slots.
  */
 export function formatTime(isoString: string): string {
   const d = new Date(isoString);
-  return d.toLocaleTimeString("en-US", { 
-    hour: "2-digit", 
-    minute: "2-digit",
-    hour12: false,
-  });
+  // Use UTC methods to avoid timezone conversion
+  const hours = String(d.getUTCHours()).padStart(2, "0");
+  const minutes = String(d.getUTCMinutes()).padStart(2, "0");
+  return `${hours}:${minutes}`;
 }
 
 /**