feat: persistent Coaster Mode toggle in header top-right

- Moves the coaster toggle out of WeekNav and into the homepage header
  top-right as "🎢 Coaster Mode", alongside the parks open badge
- State is stored in localStorage ("coasterMode") so the preference
  persists across sessions and page refreshes
- Dropped the ?coasters=1 URL param entirely; the server always fetches
  both rideCounts and coasterCounts, and HomePageClient picks which to
  display client-side — no flash or server round-trip on toggle
- Individual park pages: LiveRidePanel reads localStorage on mount and
  pre-selects the Coasters Only filter when Coaster Mode is active
- Extracted HomePageClient (client component) to own the full homepage
  UI; page.tsx is now pure data-fetching

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

components/WeekNav.tsx

@@ -7,8 +7,6 @@ interface WeekNavProps {
   weekStart: string;   // YYYY-MM-DD (Sunday)
   weekDates: string[]; // 7 dates YYYY-MM-DD
   isCurrentWeek: boolean;
-  coastersOnly: boolean;
-  hasCoasterData: boolean;
 }
 
 const MONTHS = [
@@ -33,15 +31,10 @@ function shiftWeek(weekStart: string, delta: number): string {
   return d.toISOString().slice(0, 10);
 }
 
-export function WeekNav({ weekStart, weekDates, isCurrentWeek, coastersOnly, hasCoasterData }: WeekNavProps) {
+export function WeekNav({ weekStart, weekDates, isCurrentWeek }: WeekNavProps) {
   const router = useRouter();
-  const weekParam = `week=${weekStart}`;
   const nav = (delta: number) => {
-    const base = `/?week=${shiftWeek(weekStart, delta)}`;
-    router.push(coastersOnly ? `${base}&coasters=1` : base);
-  };
-  const toggleCoasters = () => {
-    router.push(coastersOnly ? `/?${weekParam}` : `/?${weekParam}&coasters=1`);
+    router.push(`/?week=${shiftWeek(weekStart, delta)}`);
   };
 
   useEffect(() => {
@@ -99,30 +92,6 @@ export function WeekNav({ weekStart, weekDates, isCurrentWeek, coastersOnly, has
       >
         →
       </button>
-
-      {hasCoasterData && (
-        <button
-          onClick={toggleCoasters}
-          style={{
-            marginLeft: 8,
-            display: "flex",
-            alignItems: "center",
-            gap: 5,
-            padding: "4px 12px",
-            borderRadius: 20,
-            border: coastersOnly ? "1px solid var(--color-accent)" : "1px solid var(--color-border)",
-            background: coastersOnly ? "var(--color-accent-muted)" : "var(--color-surface)",
-            color: coastersOnly ? "var(--color-accent)" : "var(--color-text-muted)",
-            fontSize: "0.72rem",
-            fontWeight: 600,
-            cursor: "pointer",
-            transition: "background 150ms ease, border-color 150ms ease, color 150ms ease",
-            whiteSpace: "nowrap",
-          }}
-        >
-          🎢 Coasters
-        </button>
-      )}
     </div>
   );
 }