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/HomePageClient.tsx

@@ -19,6 +19,7 @@ interface HomePageClientProps {
   data: Record<string, Record<string, DayData>>;
   rideCounts: Record<string, number>;
   coasterCounts: Record<string, number>;
+  closingParkIds: string[];
   hasCoasterData: boolean;
   scrapedCount: number;
 }
@@ -31,6 +32,7 @@ export function HomePageClient({
   data,
   rideCounts,
   coasterCounts,
+  closingParkIds,
   hasCoasterData,
   scrapedCount,
 }: HomePageClientProps) {
@@ -165,6 +167,7 @@ export function HomePageClient({
                 today={today}
                 rideCounts={activeCounts}
                 coastersOnly={coastersOnly}
+                closingParkIds={closingParkIds}
               />
             </div>
 
@@ -177,6 +180,7 @@ export function HomePageClient({
                 grouped={grouped}
                 rideCounts={activeCounts}
                 coastersOnly={coastersOnly}
+                closingParkIds={closingParkIds}
               />
             </div>
           </>