Extract duplicate date formatting functions to shared utilities

- Created frontend/app/utils/date.ts with formatDate, formatTime, formatDateTime, formatDisplayDate
- Created frontend/e2e/helpers/date.ts with formatDateLocal, getTomorrowDateStr
- Updated all frontend pages and e2e tests to use shared utilities
- Removed duplicate date formatting code from 6 files

frontend/app/booking/page.tsx

@@ -8,6 +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, formatTime } from "../utils/date";
 
 const { slotDurationMinutes, maxAdvanceDays, minAdvanceDays, noteMaxLength } = constants.booking;
 
@@ -15,24 +16,6 @@ type BookableSlot = components["schemas"]["BookableSlot"];
 type AvailableSlotsResponse = components["schemas"]["AvailableSlotsResponse"];
 type AppointmentResponse = components["schemas"]["AppointmentResponse"];
 
-// Helper to format date as YYYY-MM-DD in local timezone
-function formatDate(d: Date): string {
-  const year = d.getFullYear();
-  const month = String(d.getMonth() + 1).padStart(2, "0");
-  const day = String(d.getDate()).padStart(2, "0");
-  return `${year}-${month}-${day}`;
-}
-
-// Helper to format time from ISO string
-function formatTime(isoString: string): string {
-  const d = new Date(isoString);
-  return d.toLocaleTimeString("en-US", { 
-    hour: "2-digit", 
-    minute: "2-digit",
-    hour12: false,
-  });
-}
-
 // Get date range for booking (tomorrow to +30 days)
 function getBookableDates(): Date[] {
   const dates: Date[] = [];