feat: coaster filter toggle on homepage

- 🎢 Coasters button in nav bar (URL-driven: ?coasters=1)
- When active, swaps ride counts for coaster counts per park
- Label switches between "X rides operating" / "X coasters operating"
- Arrow key navigation preserves coaster filter state
- Only shown when coaster data exists in park-meta

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/ParkCard.tsx

@@ -8,11 +8,12 @@ interface ParkCardProps {
   parkData: Record<string, DayData>;
   today: string;
   openRideCount?: number;
+  coastersOnly?: boolean;
 }
 
 const DOW = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
 
-export function ParkCard({ park, weekDates, parkData, today, openRideCount }: ParkCardProps) {
+export function ParkCard({ park, weekDates, parkData, today, openRideCount, coastersOnly }: ParkCardProps) {
   const openDays = weekDates.filter((d) => parkData[d]?.isOpen && parkData[d]?.hoursLabel);
   const isOpenToday = openDays.includes(today);
 
@@ -90,7 +91,9 @@ export function ParkCard({ park, weekDates, parkData, today, openRideCount }: Pa
               fontWeight: 500,
               textAlign: "right",
             }}>
-              {openRideCount} {openRideCount === 1 ? "ride" : "rides"} operating
+              {openRideCount} {coastersOnly
+                ? (openRideCount === 1 ? "coaster" : "coasters")
+                : (openRideCount === 1 ? "ride" : "rides")} operating
             </div>
           )}
           </div>