Add availability calendar to property detail page

- Fetches available date ranges from /Reservations/GetAvailableDates/available/{id}
- Custom month calendar with green (available), amber (selected), gray (unavailable)
- Click start date then end date to select a range
- Validates entire range is available before confirming
- Shows selected dates and day count
- Month navigation with prev/next arrows

app/utils/api.js

@@ -128,6 +128,11 @@ export async function getTopRecommendations(count = 10) {
 
 // ─── Reservations ───
 
+export async function getAvailableDateRanges(propertyId) {
+  console.log('[API] Fetching available dates for property:', propertyId);
+  return apiFetch(`/Reservations/GetAvailableDates/available/${propertyId}`);
+}
+
 export async function getReservations() {
   return apiFetch('/Reservations/GetReservations');
 }