fix: restore arrow key week navigation; improve empty state copy

- WeekNav: add keydown listener for ArrowLeft/ArrowRight week nav
- EmptyState: replace dev-facing "No data scraped yet" + npm commands
  with customer-friendly "Schedule not available yet" message

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

components/WeekNav.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import { useEffect } from "react";
 import { useRouter } from "next/navigation";
 
 interface WeekNavProps {
@@ -35,6 +36,16 @@ export function WeekNav({ weekStart, weekDates, isCurrentWeek }: WeekNavProps) {
   const nav = (delta: number) =>
     router.push(`/?week=${shiftWeek(weekStart, delta)}`);
 
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      if (e.target instanceof HTMLInputElement || e.target instanceof HTMLTextAreaElement) return;
+      if (e.key === "ArrowLeft")  nav(-1);
+      if (e.key === "ArrowRight") nav(1);
+    };
+    window.addEventListener("keydown", onKey);
+    return () => window.removeEventListener("keydown", onKey);
+  }, [weekStart]);
+
   return (
     <div style={{ display: "flex", alignItems: "center", gap: 8 }}>
       <button