feat: amber indicator during post-close wind-down buffer

Parks in the 1-hour buffer after scheduled close now show amber instead
of green: the dot on the desktop calendar turns yellow, and the mobile
card badge changes from "Open today" (green) to "Closing" (amber).

- getOperatingStatus() replaces isWithinOperatingWindow's inline logic,
  returning "open" | "closing" | "closed"; isWithinOperatingWindow now
  delegates to it so all callers are unchanged
- closingParkIds[] is computed server-side and threaded through
  HomePageClient → WeekCalendar/MobileCardList → ParkRow/ParkCard
- New --color-closing-* CSS variables mirror the green palette in amber

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

components/MobileCardList.tsx

@@ -10,9 +10,10 @@ interface MobileCardListProps {
   today: string;
   rideCounts?: Record<string, number>;
   coastersOnly?: boolean;
+  closingParkIds?: string[];
 }
 
-export function MobileCardList({ grouped, weekDates, data, today, rideCounts, coastersOnly }: MobileCardListProps) {
+export function MobileCardList({ grouped, weekDates, data, today, rideCounts, coastersOnly, closingParkIds }: MobileCardListProps) {
   return (
     <div style={{ display: "flex", flexDirection: "column", gap: 20, paddingTop: 14 }}>
       {Array.from(grouped.entries()).map(([region, parks]) => (
@@ -54,6 +55,7 @@ export function MobileCardList({ grouped, weekDates, data, today, rideCounts, co
                 today={today}
                 openRideCount={rideCounts?.[park.id]}
                 coastersOnly={coastersOnly}
+                isClosing={closingParkIds?.includes(park.id)}
               />
             ))}
           </div>