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/ParkCard.tsx

@@ -10,11 +10,12 @@ interface ParkCardProps {
   today: string;
   openRideCount?: number;
   coastersOnly?: boolean;
+  isClosing?: boolean;
 }
 
 const DOW = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
 
-export function ParkCard({ park, weekDates, parkData, today, openRideCount, coastersOnly }: ParkCardProps) {
+export function ParkCard({ park, weekDates, parkData, today, openRideCount, coastersOnly, isClosing }: ParkCardProps) {
   const openDays = weekDates.filter((d) => parkData[d]?.isOpen && parkData[d]?.hoursLabel);
   const tzAbbr = getTimezoneAbbr(park.timezone);
   const isOpenToday = openDays.includes(today);
@@ -60,17 +61,17 @@ export function ParkCard({ park, weekDates, parkData, today, openRideCount, coas
           <div style={{ display: "flex", flexDirection: "column", alignItems: "flex-end", gap: 5, flexShrink: 0 }}>
           {isOpenToday ? (
             <div style={{
-              background: "var(--color-open-bg)",
-              border: "1px solid var(--color-open-border)",
+              background: isClosing ? "var(--color-closing-bg)" : "var(--color-open-bg)",
+              border: `1px solid ${isClosing ? "var(--color-closing-border)" : "var(--color-open-border)"}`,
               borderRadius: 20,
               padding: "4px 10px",
               fontSize: "0.65rem",
               fontWeight: 700,
-              color: "var(--color-open-text)",
+              color: isClosing ? "var(--color-closing-text)" : "var(--color-open-text)",
               whiteSpace: "nowrap",
               letterSpacing: "0.03em",
             }}>
-              Open today
+              {isClosing ? "Closing" : "Open today"}
             </div>
           ) : (
             <div style={{
@@ -89,7 +90,7 @@ export function ParkCard({ park, weekDates, parkData, today, openRideCount, coas
           {isOpenToday && openRideCount !== undefined && (
             <div style={{
               fontSize: "0.65rem",
-              color: "var(--color-open-hours)",
+              color: isClosing ? "var(--color-closing-hours)" : "var(--color-open-hours)",
               fontWeight: 500,
               textAlign: "right",
             }}>