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/utils/date.ts

@@ -46,3 +46,18 @@ export function formatDisplayDate(d: Date): string {
   return d.toLocaleDateString("en-US", { weekday: "short", month: "short", day: "numeric" });
 }
 
+/**
+ * Get date range for booking/availability (from minAdvanceDays to maxAdvanceDays).
+ * Returns an array of Date objects starting from minAdvanceDays days from today.
+ */
+export function getDateRange(minAdvanceDays: number, maxAdvanceDays: number): 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;
+}
+