Standardize time formatting and avoid string slicing

- Created formatTimeString() utility to properly parse time strings
- Replaced all .slice(0, 5) calls with proper time formatting
- Handles both 'HH:MM:SS' and 'HH:MM' formats safely
- More robust than string slicing

frontend/app/admin/availability/page.tsx

@@ -8,7 +8,7 @@ import { Header } from "../../components/Header";
 import { useRequireAuth } from "../../hooks/useRequireAuth";
 import { components } from "../../generated/api";
 import constants from "../../../../shared/constants.json";
-import { formatDate, formatDisplayDate, getDateRange } from "../../utils/date";
+import { formatDate, formatDisplayDate, getDateRange, formatTimeString } from "../../utils/date";
 
 const { slotDurationMinutes, maxAdvanceDays, minAdvanceDays } = constants.booking;
 
@@ -87,8 +87,8 @@ export default function AdminAvailabilityPage() {
     setEditSlots(
       existingSlots.length > 0
         ? existingSlots.map((s) => ({
-            start_time: s.start_time.slice(0, 5),
+            start_time: formatTimeString(s.start_time),
-            end_time: s.end_time.slice(0, 5),
+            end_time: formatTimeString(s.end_time),
           }))
         : [{ start_time: "09:00", end_time: "17:00" }]
     );
@@ -206,7 +206,7 @@ export default function AdminAvailabilityPage() {
   };
 
   const formatSlotTime = (slot: TimeSlot): string => {
-    return `${slot.start_time.slice(0, 5)} - ${slot.end_time.slice(0, 5)}`;
+    return `${formatTimeString(slot.start_time)} - ${formatTimeString(slot.end_time)}`;
   };
 
   if (isLoading) {

frontend/app/utils/date.ts

@@ -46,6 +46,19 @@ export function formatDisplayDate(d: Date): string {
   return d.toLocaleDateString("en-US", { weekday: "short", month: "short", day: "numeric" });
 }
 
+/**
+ * Format time string from "HH:MM:SS" or "HH:MM" format to "HH:MM".
+ * Avoids string slicing by properly parsing the time.
+ */
+export function formatTimeString(timeStr: string): string {
+  // Handle both "HH:MM:SS" and "HH:MM" formats
+  const parts = timeStr.split(":");
+  if (parts.length >= 2) {
+    return `${parts[0].padStart(2, "0")}:${parts[1].padStart(2, "0")}`;
+  }
+  return timeStr;
+}
+
 /**
  * Get date range for booking/availability (from minAdvanceDays to maxAdvanceDays).
  * Returns an array of Date objects starting from minAdvanceDays days from today.