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/MobileCardList.tsx

@@ -9,9 +9,10 @@ interface MobileCardListProps {
   data: Record<string, Record<string, DayData>>;
   today: string;
   rideCounts?: Record<string, number>;
+  coastersOnly?: boolean;
 }
 
-export function MobileCardList({ grouped, weekDates, data, today, rideCounts }: MobileCardListProps) {
+export function MobileCardList({ grouped, weekDates, data, today, rideCounts, coastersOnly }: MobileCardListProps) {
   return (
     <div style={{ display: "flex", flexDirection: "column", gap: 20, paddingTop: 14 }}>
       {Array.from(grouped.entries()).map(([region, parks]) => (
@@ -52,6 +53,7 @@ export function MobileCardList({ grouped, weekDates, data, today, rideCounts }:
                 parkData={data[park.id] ?? {}}
                 today={today}
                 openRideCount={rideCounts?.[park.id]}
+                coastersOnly={coastersOnly}
               />
             ))}
           </div>