Extract duplicate date range helpers to shared utility

- Created getDateRange() function in utils/date.ts
- Replaced getBookableDates() and getDateRange() duplicates
- Both booking and availability pages now use shared function
- Function accepts minAdvanceDays and maxAdvanceDays as parameters

frontend/app/booking/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, formatTime } from "../utils/date";
+import { formatDate, formatTime, getDateRange } from "../utils/date";
 
 const { slotDurationMinutes, maxAdvanceDays, minAdvanceDays, noteMaxLength } = constants.booking;
 
@@ -16,18 +16,6 @@ type BookableSlot = components["schemas"]["BookableSlot"];
 type AvailableSlotsResponse = components["schemas"]["AvailableSlotsResponse"];
 type AppointmentResponse = components["schemas"]["AppointmentResponse"];
 
-// Get date range for booking (tomorrow to +30 days)
-function getBookableDates(): Date[] {
-  const dates: Date[] = [];
-  const today = new Date();
-  for (let i = minAdvanceDays; i <= maxAdvanceDays; i++) {
-    const d = new Date(today);
-    d.setDate(today.getDate() + i);
-    dates.push(d);
-  }
-  return dates;
-}
-
 const styles: Record<string, React.CSSProperties> = {
   main: {
     minHeight: "100vh",
@@ -244,7 +232,7 @@ export default function BookingPage() {
   const [error, setError] = useState<string | null>(null);
   const [successMessage, setSuccessMessage] = useState<string | null>(null);
 
-  const dates = getBookableDates();
+  const dates = getDateRange(minAdvanceDays, maxAdvanceDays);
 
   const fetchSlots = useCallback(async (date: Date) => {
     setIsLoadingSlots(true);