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>

lib/env.ts

@@ -55,10 +55,21 @@ export function getTimezoneAbbr(timezone: string): string {
  * compared to Pacific time regardless of where the server is running.
  */
 export function isWithinOperatingWindow(hoursLabel: string, timezone: string): boolean {
+  return getOperatingStatus(hoursLabel, timezone) !== "closed";
+}
+
+/**
+ * Returns the park's current operating status relative to its scheduled hours:
+ *   "open"    — within the scheduled open window
+ *   "closing" — past scheduled close but within the 1-hour wind-down buffer
+ *   "closed"  — outside the window entirely
+ * Falls back to "open" when the label can't be parsed.
+ */
+export function getOperatingStatus(hoursLabel: string, timezone: string): "open" | "closing" | "closed" {
   const m = hoursLabel.match(
     /^(\d+)(?::(\d+))?(am|pm)\s*[–-]\s*(\d+)(?::(\d+))?(am|pm)$/i
   );
-  if (!m) return true;
+  if (!m) return "open";
   const toMinutes = (h: string, min: string | undefined, period: string) => {
     let hours = parseInt(h, 10);
     const minutes = min ? parseInt(min, 10) : 0;
@@ -80,5 +91,7 @@ export function isWithinOperatingWindow(hoursLabel: string, timezone: string): b
   const min = parseInt(parts.find((p) => p.type === "minute")?.value ?? "0", 10);
   const nowMin = (h % 24) * 60 + min;
 
-  return nowMin >= openMin && nowMin <= closeMin + 60;
+  if (nowMin >= openMin && nowMin <= closeMin) return "open";
+  if (nowMin > closeMin && nowMin <= closeMin + 60) return "closing";
+  return "closed";
 }