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/WeekCalendar.tsx

@@ -10,7 +10,8 @@ interface WeekCalendarProps {
   weekDates: string[]; // 7 dates, YYYY-MM-DD, Sun–Sat
   data: Record<string, Record<string, DayData>>; // parkId → date → DayData
   grouped?: Map<Region, Park[]>; // pre-grouped parks (if provided, renders region headers)
-  rideCounts?: Record<string, number>; // parkId → open ride count for today
+  rideCounts?: Record<string, number>; // parkId → open ride/coaster count for today
+  coastersOnly?: boolean;
 }
 
 const DOW = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
@@ -165,6 +166,7 @@ function ParkRow({
   parsedDates,
   parkData,
   rideCounts,
+  coastersOnly,
 }: {
   park: Park;
   parkIdx: number;
@@ -172,6 +174,7 @@ function ParkRow({
   parsedDates: ReturnType<typeof parseDate>[];
   parkData: Record<string, DayData>;
   rideCounts?: Record<string, number>;
+  coastersOnly?: boolean;
 }) {
   const rowBg = parkIdx % 2 === 0 ? "var(--color-bg)" : "var(--color-surface)";
   return (
@@ -221,7 +224,9 @@ function ParkRow({
           </div>
           {rideCounts?.[park.id] !== undefined && (
             <div style={{ fontSize: "0.72rem", color: "var(--color-open-hours)", fontWeight: 600, whiteSpace: "nowrap", flexShrink: 0 }}>
-              {rideCounts[park.id]} {rideCounts[park.id] === 1 ? "ride" : "rides"} operating
+              {rideCounts[park.id]} {coastersOnly
+                ? (rideCounts[park.id] === 1 ? "coaster" : "coasters")
+                : (rideCounts[park.id] === 1 ? "ride" : "rides")} operating
             </div>
           )}
         </Link>
@@ -238,7 +243,7 @@ function ParkRow({
   );
 }
 
-export function WeekCalendar({ parks, weekDates, data, grouped, rideCounts }: WeekCalendarProps) {
+export function WeekCalendar({ parks, weekDates, data, grouped, rideCounts, coastersOnly }: WeekCalendarProps) {
   const today = getTodayLocal();
   const parsedDates = weekDates.map(parseDate);
 
@@ -353,6 +358,7 @@ export function WeekCalendar({ parks, weekDates, data, grouped, rideCounts }: We
                   parsedDates={parsedDates}
                   parkData={data[park.id] ?? {}}
                   rideCounts={rideCounts}
+                  coastersOnly={coastersOnly}
                 />
               ))}
             </Fragment>